Patent Publication Number: US-2023141256-A1

Title: Display device on/off detection methods and apparatus

Description:
RELATED APPLICATIONS 
     This patent arises from a continuation of U.S. patent application Ser. No. 17/164,483 (now U.S. Pat. No. ______), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Feb. 1, 2021, which is a continuation of U.S. patent application Ser. No. 16/706,280 (now U.S. Pat. No. 10,911,749), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Dec. 6, 2019, which is a continuation of U.S. patent application Ser. No. 16/417,128 (now U.S. Pat. No. 10,506,226), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on May 20, 2019, which is a continuation of U.S. patent application Ser. No. 16/166,871 (now U.S. Pat. No. 10,306,221), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Oct. 22, 2018, which is a continuation of U.S. patent application Ser. No. 15/958,814 (now U.S. Pat. No. 10,110,889), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Apr. 20, 2018, which is a continuation of U.S. patent application Ser. No. 15/207,019 (now U.S. Pat. No. 9,961,342), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Jul. 11, 2016, which is a continuation of U.S. patent application Ser. No. 14/015,664 (now U.S. Pat. No. 9,420,334), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Aug. 30, 2013, which is a continuation of U.S. patent application Ser. No. 12/831,870 (now U.S. Pat. No. 8,526,626), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Jul. 7, 2010, which is a continuation of U.S. patent application Ser. No. 11/576,328 (now U.S. Pat. No. 7,882,514), titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Mar. 29, 2007, which is a U.S. national stage of International Patent Application No. PCT/US2006/031960, titled “Display Device ON/OFF Detection Methods and Apparatus,” filed on Aug. 16, 2006, which claims the benefit of U.S. Provisional Application No. 60/708,557, titled “Display Device ON/OFF Detection Methods and Apparatus” and filed on Aug. 16, 2005, and U.S. Provisional Application No. 60/761,678, titled “Display Device ON/OFF Detection Methods and Apparatus” and filed on Jan. 24, 2006. Priority to U.S. Provisional Application No. 60/708,557, U.S. Provisional Application No. 60/761,678, International Application No. PCT/US2006/031960, U.S. patent application Ser. No. 11/576,328, U.S. patent application Ser. No. 12/831,870, U.S. patent application Ser. No. 14/015,664, U.S. patent application Ser. No. 15/207,019, U.S. patent application Ser. No. 15/958,814, U.S. patent application Ser. No. 16/166,871, U.S. patent application Ser. No. 16/417,128, U.S. patent application Ser. No. 16/706,280 and U.S. patent application Ser. No. 17/164,483 is hereby claimed. U.S. Provisional Application No. 60/708,557, U.S. Provisional Application No. 60/761,678, International Application No. PCT/US2006/031960, U.S. patent application Ser. No. 11/576,328, U.S. patent application Ser. No. 12/831,870, U.S. patent application Ser. No. 14/015,664, U.S. patent application Ser. No. 15/207,019, U.S. patent application Ser. No. 15/958,814, U.S. patent application Ser. No. 16/166,871, U.S. patent application Ser. No. 16/417,128, U.S. patent application Ser. No. 16/706,280 and U.S. patent application Ser. No. 17/164,483 are hereby incorporated by reference in their respective entireties. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to audience measurement and, more particularly, to display device ON/OFF detection methods and apparatus. 
     BACKGROUND 
     Media ratings and metering information is typically generated by collecting viewing records and/or other media consumption information from a group of statistically selected households. Each of the statistically selected households typically has a data logging and processing unit commonly referred to as a “home unit.” In households having multiple viewing sites (e.g., multiple television systems or, more generally, multiple presentation devices), the data logging and processing functionality may be distributed among a single home unit and multiple “site units,” one site unit for each viewing site. The home unit (or the combination of the home unit and the site unit) is often in communication with a variety of attachments that provide inputs to the home unit or receive outputs from the metering unit. For example, a frequency detector attachment coupled with the home unit may be in communication with a television to sense a local oscillator frequency of the television tuner. In this manner, the frequency detector attachment may be used by the home unit to determine the channel to which the television is currently tuned based on a detected frequency. As another example, a people meter may be located in the viewing space of the television and in communication with the home unit, thereby enabling the home unit to detect the identities and/or number of the persons currently viewing programs displayed on the television. Additional devices may be provided, for example, to determine if the television is operating (i.e., is turned ON) and/or the channel to which the television is tuned. 
     In addition, building security and building monitoring systems are becoming more and more prevalent in today&#39;s society. Such systems enable the building owner to determine the status of various electronic appliances disposed in the building even when the building owner is located remotely from the building premises. In many instances, the building owner may desire to know the operating status, e.g., ON/OFF, of a particular appliance, such as a television, or other media delivery/presentation device. 
     In another setting, parents often have an interest in monitoring their children&#39;s television viewing habits, electronic gaming habits and computer usage habits. A component of monitoring such habits involves determining the operating status of the appliance, electronic device, etc. of interest. 
     Media monitoring systems, building monitoring systems and parenting tools such as those described above, are only three (of many) applications in which an ON/OFF detection apparatus/device has use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an example local metering system including an example display device ON/OFF detector and shown coupled to an example home entertainment system. 
         FIG.  2    is a block diagram of the example display device ON/OFF detector of  FIG.  1   . 
         FIG.  3    is a block diagram of an example set of audio processors that may be used to implement the example display device ON/OFF detector of  FIG.  2   . 
         FIG.  4    is a block diagram of an example set of video processors that may be used to implement the example display device ON/OFF detector of  FIG.  2   . 
         FIG.  5    is a block diagram of an example set of emissions processor that may be used to implement the example display device ON/OFF detector  FIG.  2   . 
         FIG.  6    is a block diagram of a first example audio processor system that may be used to implement one or more of the example audio processors of  FIG.  3   . 
         FIG.  7    is a block diagram of a second example audio processor system that may be used to implement one or more of the example audio processors of  FIG.  3   . 
         FIG.  8    is a block diagram of an example video processor system that may be used to implement one or more of the example video processors of  FIG.  4   . 
         FIGS.  9 A-B  are block diagrams of two implementations of a first example emission processor system that may be used to implement the example electromagnetic field detector of  FIG.  5   . 
         FIG.  10    is a block diagram of a second example emission processor system that may be used to implement the current detector of  FIG.  5   . 
         FIG.  11    is a block diagram of a third example emission processor system that may be used to implement the temperature detector of  FIG.  5   . 
         FIGS.  12 A-C  are block diagrams of fourth, fifth and sixth example emission processor systems that may be used to implement the remote control activity detector and/or the people meter activity detector of  FIG.  5   . 
         FIG.  13    is a flowchart representative of example machine readable instructions that may be executed to implement the example audio code detector of  FIG.  3   . 
         FIG.  14    is a flowchart representative of first example machine readable instructions that may be executed to implement the example audio signature processor of  FIG.  3   . 
         FIG.  15    is a flowchart representative of second example machine readable instructions that may be executed to implement the example audio signature processor of  FIG.  3   . 
         FIG.  16    is a flowchart representative of example machine readable instructions that may be executed to implement the example audio gain level processor of  FIG.  3   . 
         FIG.  17    is a flowchart representative of example machine readable instructions that may be executed to implement the example horizontal sync audio processor of  FIG.  3   . 
         FIG.  18    is a flowchart representative of example machine readable instructions that may be executed to implement the example quiet time detector of  FIG.  3   . 
         FIG.  19    is a flowchart representative of example machine readable instructions that may be executed to implement the example fan noise detector of  FIG.  3   . 
         FIG.  20    is a flowchart representative of example machine readable instructions that may be executed to implement the example audio source detector of  FIG.  3   . 
         FIG.  21    is a flowchart representative of example machine readable instructions that may be executed to implement the example visible light rhythm processor of  FIG.  4   . 
         FIG.  22    is a flowchart representative of example machine readable instructions that may be executed to implement the example display activity detector of  FIG.  4   . 
         FIG.  23    is a flowchart representative of example machine readable instructions that may be executed to implement the example electromagnetic field detector of  FIG.  5   . 
         FIG.  24    is a flowchart representative of example machine readable instructions that may be executed to implement the example current detector of  FIG.  5   . 
         FIG.  25    is a flowchart representative of example machine readable instructions that may be executed to implement the example temperature detector of  FIG.  5   . 
         FIG.  26    is a flowchart representative of example machine readable instructions that may be executed to implement the example remote control activity detector and/or the people meter activity detector of  FIG.  5   . 
         FIG.  27    is a flowchart representative of first example machine readable instructions that may be executed to implement the example decision processor of  FIG.  2   . 
         FIG.  28    is a flowchart representative of second example machine readable instructions that may be executed to implement the example decision processor of  FIG.  2   . 
         FIG.  29    is a block diagram of an example computer that may execute the example machine readable instructions of  FIGS.  13 - 26  and/or  27    to implement the example display device ON/OFF detector of  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     A block diagram of an example local metering system  100  capable of providing viewing and metering information for program content presented via an example home entertainment system  102  is illustrated in  FIG.  1   . The example home entertainment system  102  includes a broadcast source  104 , a set-top box (STB)  108 , a signal splitter  116  and a display device  120 . The example local metering system  100  includes a metering unit  124  and a display device ON/OFF detector  128 . The components of the home entertainment system  102  and the local metering system  100  may be connected in any well-known manner including that shown in  FIG.  1   . For example, in a statistically selected household having one or more home entertainment systems  102 , the metering unit  124  may be implemented as a single home unit and one or more site units. In such a configuration, the single home unit may perform the functions of storing data and forwarding the stored data to a central facility for subsequent processing. Each site unit is coupled to a corresponding home entertainment system  102  and performs the functions of collecting viewing/metering data, processing such data (possibly in real-time) and sending the processed data to the single home unit for that home. The home unit receives and stores the data collected by the site units and subsequently forwards that collected data to the central facility. 
     The broadcast source  104  may be any broadcast media source, such as a cable television service provider, a satellite television service provider, a radio frequency (RF) television service provider, an internet streaming video/audio provider, etc. The broadcast source  104  may provide analog and/or digital television signals to the home entertainment system  102 , for example, over a coaxial cable or via a wireless connection. 
     The STB  108  may be any set-top box, such as a cable television converter, a direct broadcast satellite (DBS) decoder, a video cassette recorder (VCR), etc. The set-top box  108  receives a plurality of broadcast channels from the broadcast source  104 . Typically, the STB  108  selects one of the plurality of broadcast channels based on a user input, and outputs one or more signals received via the selected broadcast channel. In the case of an analog signal, the STB  108  tunes to a particular channel to obtain programming delivered on that channel. For a digital signal, the STB  108  may tune to a channel and decode certain packets of data to obtain programming delivered on a selected channel. For example, the STB  108  may tune to a major channel and then extract a program carried on a minor channel within the major channel via the decoding process mentioned above. For some home entertainment systems  102 , for example, those in which the broadcast source  104  is a standard RF analog television service provider or a basic analog cable television service provider, the STB  108  may not be present as its function is performed by a tuner in the display device  120 . 
     In the illustrated example, an output from the STB  108  is fed to a signal splitter  116 , such as a single analog y-splitter (in the case of an RF coaxial connection between the STB  108  and the display device  120 ) or an audio/video splitter (in the case of a direct audio/video connection between the STB  108  and the display device  120 ). (For configurations in which the STB  108  is not present, the broadcast source  104  may be coupled directly to the signal splitter  116 ). In the example home entertainment system  102 , the signal splitter produces two signals indicative of the output from the STB  108 . Of course, a person of ordinary skill in the art will readily appreciate that any number of signals may be produced by the signal splitter  116 . 
     In the illustrated example, one of the two signals from the signal splitter  116  is fed to the display device  120  and the other signal is delivered to the metering unit  124 . The display device  120  may be any type of video display device, such as a television. For example, the display device  120  may be a television and/or other display device (e.g., a computer monitor, a CRT, an LCD, etc.) that supports the National Television Standards Committee (NTSC) standard, the Phase Alternating Line (PAL) standard, the Systéme Èlectronique pour Couleur avec Mémoire (SECAM) standard, a standard developed by the Advanced Television Systems Committee (ATSC), such as high definition television (HDTV), a standard developed by the Digital Video Broadcasting (DVB) Project, or may be a multimedia computer system, etc. 
     In the example of  FIG.  1   , the second of the two signals from the signal splitter  116  (i.e., the signal carried by connection  136  in  FIG.  1   ) is coupled to an input of the metering unit  124 . The metering unit  124  is a data logging and processing unit that may be used to generate viewing records and other viewing information useful for determining viewing and other metering information. The metering unit  124  typically collects a set of viewing records and transmits the collected viewing records over a connection  140  to a central office or data processing facility (not shown) for further processing or analysis. The connection  140  may be a telephone line, a return cable television connection, an RF or satellite connection, an internet connection or the like. 
     The metering unit  124  may be configured to determine identifying information based on the signal corresponding to the program content being output by the STB  108 . For example, the metering unit  124  may be configured to decode an embedded code in the signal received via connection  136  that corresponds to the channel or program currently being delivered by the STB  108  for display on the display device  120 . The code may be embedded for purposes such as, for example, audience measurement, program delivery (e.g., PIDS in a digital television presentation, electronic program guide information, etc.) or delivery of other services (e.g., embedded hyperlinks to related programming, closed caption information, etc.). Alternatively or additionally, the metering unit  124  may be configured to generate a program signature (e.g., a proxy signal which is uniquely representative of the program, signal) based on the signal received via connection  136  that corresponds to the program currently being delivered by the STB  108  for display on the display device  120 . The metering unit  124  may then add this program identifying information (e.g., the code(s) and/or signature(s)) to the viewing records corresponding to the currently displayed program. 
     In the example local metering system  100 , the display device ON/OFF detector  128  is coupled to the metering unit  124 . The display device ON/OFF detector  128  is configured to determine whether the display device  120  or other monitored information presenting device (e.g., a computer monitor, etc.) is operating in an ON (active) state or an OFF (inactive) state. Such ON/OFF detection information concerning the operating state of the information presenting device  120  may be used to more accurately process the viewing information and viewing records determined by the metering unit  124 . For example, in the home entertainment system  102 , it is possible that even though the display device  120  is turned OFF, the STB  108  may be inadvertently or intentionally left in an ON (active) state such that the STB  108  continues to receive and output program content provided by the broadcast source  104 . Without the ON/OFF detection information provided by the display device ON/OFF detector  128 , the metering unit  124  (or subsequent processing at, for example, a central facility) might credit the program content provided by the STB  108  as being consumed even though the display device  120  is turned OFF. Thus, the display device ON/OFF detector  128  may be used to augment the viewing information and/or viewing records determined by the metering unit  124  to more accurately determine whether program content output by the STB  108  is actually presented by the display device  120 . 
     To facilitate the determination of program identifying information and the generation of viewing records for the program content received and output by the STB  108 , as well as the determination of the operating state of the display device  120  or corresponding information presenting device, the metering unit  124  and the display device ON/OFF detector  128  may be provided with one or more sensors  144 . For example, a sensor  144  may be implemented by a microphone placed in the proximity of the display device  120  to receive audio signals corresponding to the program being displayed. The metering unit  124  and/or display device ON/OFF detector  128  may then process the audio signals received from the microphone  144  to decode any embedded ancillary code(s) and/or generate one or more audio signatures corresponding to a program being displayed. The display device ON/OFF detector  128  may also process the audio signal to determine whether the display device  120  is turned ON and emitting audio signals consistent with operation in an active state. 
     Additionally or alternatively, a sensor  144  may be implemented by an on-screen display detector for capturing images displayed on the display device  120  and processing regions of interest in the displayed image. The regions of interest may correspond, for example, to a broadcast channel associated with the currently displayed program, a broadcast time associated with the currently displayed program, a viewing time associated with the currently displayed program, etc. Example on-screen display detectors are disclosed by Nelson, et al. in U.S. Provisional Patent Application Ser. No. 60/523,444 filed on Nov. 19, 2003, and Patent Cooperation Treaty Application Serial No. PCT/US04/12272 filed on Apr. 19, 2004, both of which are hereby incorporated by reference. 
     Additionally or alternatively, a sensor  144  could be implemented by a frequency detector to determine, for example, the channel to which the display device  120  is tuned. Additionally or alternatively, a sensor  144  could be implemented by an electromagnetic (EM) field pickup, a current sensor and/or a temperature sensor configured to detect emissions from the display device  120  indicative of the display device  120  being turned ON. Persons having ordinary skill in the art will recognize that there are a variety of sensors  144  that may be coupled with the metering unit  124  and/or the display device ON/OFF detector to facilitate generation of viewing records and display device operating state data containing sufficient information to determine a set of desired ratings and/or metering results. Persons of ordinary skill in the art will also appreciate that any or all of the sensors  144  may be located separate from and/or disposed in the metering unit  124 , the display device ON/OFF detector  128  and/or any combination thereof. Additionally or alternatively, any or all of the sensors  144  may be duplicated in the metering unit  124  and the display device ON/OFF detector  128  to, for example, facilitate flexible placement of the various components of the local metering system  100  to permit metering of a wide range of home entertainment systems  102 . 
     The example home entertainment system  102  of  FIG.  1    also includes a remote control device  160  to transmit control information that may be received by any or all of the STB  108 , the display device  120 , the metering unit  124  and/or the display device ON/OFF detector  128 . Persons having ordinary skill in the art will recognize that the remote control device  160  may transmit this information using a variety of techniques, including, but not limited to, infrared (IR) transmission, ultrasonic transmission, radio frequency transmission, wired/cabled connection, and the like. 
     The example local metering system  100  of  FIG.  1    also includes a people meter  162  to capture information about the audience. The example people meter  162  may be configured to receive information from a people meter control device  164  having a set of input keys, each assigned to represent a single viewer. The people meter  162  may prompt the audience members to indicate that they are present in the viewing audience by pressing the appropriate input key on the people meter control device  164 . The people meter  162  may also receive information from the metering unit  124  to determine a time at which to prompt the audience members. Moreover, the metering unit  124  may receive information from the people meter  162  and/or the people meter control device  164  to modify an operation of the metering unit  124  (e.g., such as causing the metering unit  124  to generate one or more viewing records based on a change in the viewing audience). The display device ON/OFF detector  128  may also receive information from the people meter  162  and/or people meter control device  164  to facilitate determination of whether the display device  120  is currently turned ON (e.g., such as receiving responses to prompts displayed by the display device  120 ). As will be appreciated by persons having ordinary skill in the art, the people meter control device  164  may transmit and/or receive information using a variety of techniques, including, but not limited to, infrared (IR) transmission, radio frequency transmission, ultrasonic transmission, wired/cabled connection, and the like. As will also be appreciated by persons having ordinary skill in the art, the people meter control device  164  and people meter  162  may be implemented by a combination of the remote control device  160  and one or more of the STB  108  and/or the metering unit  124 . In such an implementation, the STB  108  and/or the metering unit  124  may be configured to display prompting information and/or other appropriate people meter content directly on the display device  120 . Correspondingly, the remote control device  160  may be configured to accept inputs from the viewing audience and transmit these user inputs to the appropriate device responsible for generating the people meter display on the display device  120 . 
     Persons of ordinary skill in the art will appreciate that the metering unit  124  and the display device ON/OFF detector  128  may be implemented as separate devices or integrated into a single unit. Additionally or alternatively, any or all or the metering unit  124 , the display device ON/OFF detector  128 , or portions thereof may be integrated into the STB  108  and/or the display device  120 . For example, the display device ON/OFF detector  128  could be integrated into the STB  108  such that STB  108  is able to determine whether program content being received and output is also being presented by the monitored display device  120  or corresponding information presenting device. Such display device operating state information, coupled with operating state information concerning the STB  108  itself, could be transmitted back to the broadcast provider responsible for the broadcast source  104  via a back-channel connection  168  to allow the broadcast provider to, for example, monitor consumption of program content output by the STB  108  and presented by the display device  120  in the absence of the metering unit  124 . 
     A block diagram of an example display device ON/OFF detector  200  that may be used to implement the display device ON/OFF detector  128  of  FIG.  1    is illustrated in  FIG.  2   . The example display device ON/OFF detector  200  is configured to process signals received from one or more sensors, such as the sensors  144  of  FIG.  1   . In the example of  FIG.  2   , the display device ON/OFF detector  200  includes an audio sensor  204 , a video sensor  208  and an emission sensor  212 . The audio sensor  204  may be one or more microphones positioned to detect audio signals emitted by the display device  120  or corresponding information presenting device. The video sensor  208  may be, for example, a camera, a single output analog or digital light sensor, etc., positioned to detect the display area of the display device  120  or corresponding information presenting device. The emission sensor  212  may include one or more sensors configured to detect emissions from the display device  120  or corresponding information presenting device, or emissions from other devices that may be indicative of the operating state of the display device  120  or corresponding information presenting device. For example, the emission sensor  212  may include an EM field pickup to detect EM emissions from the display device  120 , a current detector to detect current draw from a power source coupled to the display device  120 , a temperature sensor to detect heat radiated by the display device  120 , a receiver to detect control signals from, for example, the remote control device  160  and/or people meter control device  164  indicative of an active display device  120 , etc. 
     The display device ON/OFF detector  200  includes one or more audio processors  228  to process the audio signal  230  output by the audio sensor  224 . The audio processors  228  are configured to determine characteristics of the input audio signal  230  and/or information included in the input audio signal  230  that may be used to ascertain whether the monitored information presenting is turned ON and operating in an active state. Examples of audio processors  228  are discussed in greater detail below in connection with  FIG.  3   . 
     The example display device ON/OFF detector  200  also includes one or more video processors  232  to process the video signal  234  output by the video sensor  208 . Similar to the audio processors  228 , the video processors  232  are configured to determine characteristics of the input video signal  234  and/or information included in the input video signal  234  that may be used to ascertain whether the information presenting device monitored by the display device ON/OFF detector  200  (e.g., the display device  120 ) is turned ON and operating in an active state. Examples of video processors  232  are discussed in greater detail below in connection with  FIG.  4   . 
     The example display device ON/OFF detector  200  also includes one or more emission processors  236  to process the emission signals  238  output by the emission sensor  212 . Similar to the audio processors  228  and the video processors  232 , the emission processors  236  are configured to determine characteristics of the input emission signals  238  and/or information included in the input emission signals  238  that may be used to ascertain whether the information presenting device monitored by the display device ON/OFF detector  200  (e.g., the display device  120 ) is turned ON and operating in an active state. Examples of emission processors  236  are discussed in greater detail below in connection with  FIG.  5   . 
     The example display device ON/OFF detector  200  of  FIG.  2    includes a decision processor  244  to process the ON/OFF decision outputs  246 ,  248  and  250  generated by the audio processor(s)  228 , the video processor(s)  232  and/or the emission processor(s)  236 , if present. The decision processor  244  processes the available input information to determine whether the information presenting device monitored by the display device ON/OFF detector  200  (e.g., the display device  120 ) is turned ON and operating in an active state. The decision processor  244  outputs its ON/OFF decision via the device ON/OFF decision output  254 . An example set of machine readable instructions which may be executed to implement the decision processor  244  is discussed in greater detail below in connection with  FIG.  27   . 
     An example set of audio processors  228  is shown in  FIG.  3   . The audio processors  228  process the input audio signal(s)  230  provided, for example, by the audio sensor(s)  204  of  FIG.  2   . The input audio signal(s)  230  are intended to correspond to an audio signal being output by a monitored information presenting device, such as the display device  120  of  FIG.  1   . A particular audio processor in the set of audio processors  228  may be configured to sample and process the input audio signal  230  at a frequency that depends on the processing performed by that particular audio processor. Thus, the audio processors  228  may operate autonomously and read the input audio signal  230  and generate corresponding audio processor outputs  246  in an autonomous fashion. 
     The example set of audio engines  228  of  FIG.  3    includes an audio code detector  312 , an audio signature processor  316 , an audio gain level processor  320 , a horizontal sync audio processor  324 , a quiet time detector  328 , a fan noise processor  332  and an audio source detector  336 . The example audio code detector  312  is configured to detect audio codes that may be embedded in the audio signal corresponding to the input audio signal  230 . As is known, audio codes may be used to encode and embed identifying information (e.g., a broadcast/network channel number, a program identification code, a broadcast time stamp, a source identifier to identify a network and/or station providing and/or broadcasting the content, etc.) in, for example, non-audible portions of the audio signal accompanying a broadcast program. Methods and apparatus for implementing the audio code detector  312  are known in the art. For example, in U.S. Pat. No. 6,272,176, incorporated herein by reference in its entirety, Srinivasan discloses a broadcast encoding system and method for encoding and decoding information transmitted within an audio signal. This and/or any other appropriate technique may be used to implement the audio code detector  312 . Additionally, example machine readable instructions  1300  that may be executed to implement the audio code detector  312  are discussed in the detailed description of  FIG.  13    below. 
     The example audio signature processor  316  of  FIG.  3    is configured to generate and process audio signatures corresponding to the input audio signal  230 . As is known, characteristics of the audio portion of presented program content may be used to generate a substantially unique proxy or signature (e.g., a series of digital values, a waveform, etc.) for that content. The signature information for the content being presented may be compared to a set of reference signatures corresponding to a known set of content. When a substantial match is found, the currently presented program content can be identified with a relatively high probability. Methods and apparatus for implementing the audio signature processor  316  are known in the art. For example, in U.S. patent application Ser. No. 09/427,970, incorporated herein by reference in its entirety, Srinivasan, et al. disclose audio signature extraction and correlation techniques. As another example, in Patent Cooperation Treaty Application Serial No. PCT/US03/22562, incorporated herein by reference in its entirety, Lee, et al. disclose signature based program identification apparatus and methods for use with a digital broadcast system. These and/or any other appropriate technique may be used to implement the audio signature processor  316 . Additionally, example machine readable instructions  1400  and  1500  that may be executed to implement the audio signature processor  316  are discussed in the detailed description of  FIGS.  14 - 15    below. 
     The example audio gain level processor  320  of  FIG.  3    is configured to determine the amount of amplifier gain applied to the input audio signal  230  to appropriately fill the dynamic range of an analog-to-digital converter used to sample the input audio signal  230  for processing by the various audio signal processors  228 . Knowledge of the amount of gain applied to the input audio signal  230  may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON and emitting an audio signal. Example machine readable instructions  1600  that may be executed to implement the audio gain level processor  320  are discussed in the detailed description of  FIG.  16    below. 
     The example horizontal sync audio processor  324  of  FIG.  3    is configured to determine whether the input audio signal  230  includes audio emissions generated by a horizontal scan fly-back transformer used to scan an electron beam across a picture tube of a monitored information presenting device, such as the display device  120  of  FIG.  1   . For example, in a display device  120  operating in accordance with the NTSC standard, the laminations of the fly-back transformer emit a tonal audio signal at approximately 15.75 kHz. Knowledge of the whether the input audio signal  230  includes audio emission corresponding to the horizontal scan fly-back transformer may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON. Methods and apparatus which may be adapted to implement the horizontal sync audio processor  324  are known in the art. For example, Patent Cooperation Treaty Application Serial No. PCT/US02/12333, incorporated herein by reference in its entirety, discloses a television proximity sensor based on monitoring the audio signal emitted by a horizontal scan fly-back transformer. This and/or any other appropriate technique may be used to implement the horizontal sync audio processor  324 . Additionally, example machine readable instructions  1700  that may be executed to implement the horizontal sync audio processor  324  are discussed in the detailed description of  FIG.  17    below. 
     The example quiet time detector  328  of  FIG.  3    is configured to determine whether the input audio signal  230  includes quiet time characteristics typically associated with, for example, broadcast channel change events, etc. Knowledge of the whether the input audio signal  230  includes quiet time characteristics may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON based on the presence of audio indicative of the information presenting device being controlled by a user. Methods and apparatus which may be adapted to implement the quiet time detector  328  are known in the art. For example, Patent Cooperation Treaty Application Serial No. PCT/US03/27336, incorporated herein by reference in its entirety, discloses audio based methods and apparatus for detecting channel change events which employ detection of quiet-time intervals. This and/or any other appropriate technique may be used to implement the quiet time detector  328 . Additionally, example machine readable instructions  1800  that may be executed to implement the quiet time detector  328  are discussed in the detailed description of  FIG.  18    below. 
     The example fan noise detector  332  of  FIG.  3    is configured to determine whether the input audio signal  230  includes a component indicative of audio noise generated by a fan assembly operating in a monitored information presenting device. Knowledge of the whether the input audio signal  230  includes fan noise may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON based on the activation of an associated fan assembly. Example machine readable instructions  1900  that may be executed to implement the fan noise detector  332  are discussed in the detailed description of  FIG.  19    below. 
     The example audio source detector  336  of  FIG.  3    is configured to determine the location of the source of the input audio signal  230 . Knowledge of the location of the source of the input audio signal  230  may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON based on whether the determined source location coincides with the monitored information presenting device. Methods and apparatus which may be adapted to implement the audio source detector  336  are known in the art. For example, in “A Tentative Typology of Audio Source Separation Tasks,”  ICA 2003, April 2003, incorporated herein by reference in its entirety, Vincent, et al. discuss techniques for audio source separation. Additionally, in “Using IIDs to Estimate Sound Source Direction,” in  From Animals to Animats  7, edited by Hallam, et al., MIT Press, 2002, incorporated herein by reference in its entirety, Smith discusses techniques for using inter-aural intensity differences to determine audio source direction information. These and/or any other appropriate technique may be used to implement the audio source detector  336 . Additionally, example machine readable instructions  2000  that may be executed to implement the audio source detector  336  are discussed in the detailed description of  FIG.  20    below. 
     As shown in the example of  FIG.  3   , the results of each audio processor  312 - 336  may be scaled/prioritized by a set of respective weights  340 - 364 . For example, the weights  340 - 364  may explicitly scale the processor results based on the amount of information, amount of confidence, etc. that a respective result may contribute to the processing performed by a decision processor, such as the decision processor  224  of  FIG.  2   . Additionally or alternatively, the weights  340 - 364  may be implicit and based, for example, on a stage in which a particular audio processor result is used in a decision process performed by the decision processor, the priority given a particular audio processor result by the decision processor, etc. In any case, the scaling may be dynamic or static. Also, the weights  340 - 364  may be eliminated explicitly or implicitly be setting the values of the weights  340 - 364  all equal to one. 
     An example set of video processors  232  is shown in  FIG.  4   . The video processors  232  process the input video signal  234  provided, for example, by the video sensor  208  of  FIG.  2   . The input video signal  234  is intended to be representative of a display corresponding to a monitored presentation device, such as the display device  120  of  FIG.  1   . A particular video processor in the set of video processors  232  may be configured to sample and process the input video signal  234  at a frequency that depends on the processing performed by that particular video processor. Thus, the video processors  232  may operate autonomously and sample the input video signal  234  and generate corresponding video processor outputs  248  in an autonomous fashion. 
     The example set of video engines  232  of  FIG.  4    includes a visible light rhythm processor  412  and a display activity detector  416 . The example visible light rhythm processor  412  of  FIG.  4    is configured to determine whether light patterns over time associated with the input video signal  234  corresponds to patterns indicative of an active display of a monitored information presenting device. Knowledge of whether the input video signal  234  includes such light patterns may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON based on whether the light patterns are indicative of an active display device. Methods and apparatus which may be adapted to implement the visible light rhythm processor  412  are known in the art. For example, Patent Cooperation Treaty Application Serial No. PCT/US03/30370, incorporated herein by reference in its entirety, discloses methods and apparatus to detect an operating state of a display based on visible light. This and/or any other appropriate technique may be used to implement the visible light rhythm processor  412 . Additionally, example machine readable instructions  2100  that may be executed to implement the visible light rhythm processor  412  are discussed in the detailed description of  FIG.  21    below. 
     The example display activity detector  416  of  FIG.  4    is configured to determine whether a particular region of a monitored scene corresponding to the input video signal  234  varies in accordance with an active display of a monitored information presenting device. Knowledge of whether the input video signal  234  includes such varied scene activity may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON based on whether the regions of the scene associated with the display of the information presenting device indicate that the display is active. Example machine readable instructions  2200  that may be executed to implement the display activity detector  416  are discussed in the detailed description of  FIG.  22    below. 
     As shown in the example of  FIG.  4   , the results of each video processor  412 - 416  may be scaled/prioritized by a set of respective weights  432 - 436 . For example, the weights  432 - 436  may explicitly scale the video processor results based on the amount of information, amount of confidence, etc. that a respective result may contribute to the processing performed by a decision processor, such as the decision processor  224  of  FIG.  2   . Additionally or alternatively, the weights  432 - 436  may be implicit and based, for example, on a stage in which a particular video processor result is used in a decision process performed by the decision processor, the priority given a particular video processor result by the decision processor, etc. In any case, the scaling may be dynamic or static. Also, the weights  432 - 436  may be eliminated explicitly or implicitly be setting the values of the weights  432 - 436  all equal to one. 
     An example set of emissions processors  236  is shown in  FIG.  5   . The emissions processors  236  of  FIG.  5    process the input emission signals  238  provided, for example, by the emission sensors  212  of  FIG.  2   . The input emissions signals  238  are intended to correspond to one or more emissions from a monitored presentation device, such as the display device  120  of  FIG.  1   . A particular emission processor in the set of emission processors  236  may be configured to sample and process the appropriate input emission signal  238  at a frequency that depends on the processing performed by that particular emission processor. Thus, the emission processors  236  may operate autonomously and sample the appropriate input emission signal  238  and generate corresponding emission processor outputs  250  in an autonomous fashion. 
     The example set of emissions processors  236  of  FIG.  5    includes an electromagnetic (EM) field detector  512 , a current detector  516 , a temperature detector  520 , a remote control activity detector  524  and a people meter activity detector  528 . The example EM field detector  512  of  FIG.  5    is configured to process an EM field emission input  532  corresponding to an EM field measured by an appropriately configured emission sensor  212 . Knowledge of whether the EM field emission input  532  corresponds to EM field emissions from a monitored information presenting device may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether the monitored information presenting device is ON. Any known technique may be used to implement the EM field detector  512 . Additionally, example machine readable instructions  2300  that may be executed to implement the EM field detector  512  are discussed in the detailed description of  FIG.  23    below. 
     The example current detector  516  of  FIG.  5    is configured to process a current input  536  corresponding to a current measured by an appropriately configured emission sensor  212 . Knowledge of whether the current input  536  corresponds to an amount of current that would be drawn from a power source coupled to an actively-operating monitored information presenting device may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether the monitored information presenting device is ON. Any known technique may be used to implement the current detector  516 . Additionally, example machine readable instructions  2400  that may be executed to implement the current detector  516  are discussed in the detailed description of  FIG.  24    below. 
     The example temperature detector  520  of  FIG.  5    is configured to process one or more temperature inputs  540  corresponding to, for example, sensors  212  configured to measure the temperature of a monitored information presenting device and the ambient air temperature of a room in which the information presenting device is located. Knowledge of whether the temperature of the monitored information presenting device is substantially higher than the ambient air temperature may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether the monitored information presenting device is ON. Example machine readable instructions  2500  that may be executed to implement the temperature detector  520  are discussed in the detailed description of  FIG.  25    below. 
     The example remote control activity detector  524  of  FIG.  5    is configured to process a remote control signal input  544  corresponding to a received signal from an appropriately configured emission sensor  212 . Knowledge of whether the remote control signal input  544  corresponds to a valid remote control command may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON. Example machine readable instructions  2600  that may be executed to implement the remote control activity detector  524  are discussed in the detailed description of  FIG.  26    below. 
     The example people meter activity detector  528  of  FIG.  5    is configured to process a people meter signal input  548  corresponding to a received signal from an appropriately configured emission sensor  212 . Knowledge of whether the remote control signal input  544  corresponds to a valid people meter response and/or command may be used, for example, by a decision processor, such as the decision processor  244  of  FIG.  2   , to determine whether a monitored information presenting device is ON. Example machine readable instructions  2600  that may be executed to implement the people meter activity detector  528  are discussed in the detailed description of  FIG.  26    below. 
     As shown in the example of  FIG.  5   , the results of each emission processor  512 - 528  may be scaled/prioritized by a set of respective weights  552 - 568 . For example, the weights  552 - 568  may explicitly scale the emission processor results based on the amount of information, amount of confidence, etc. that a respective result may contribute to the processing performed by a decision processor, such as the decision processor  224  of  FIG.  2   . Additionally or alternatively, the weights  552 - 568  may be implicit and based, for example, on a stage in which a particular emission processor result is used in a decision process performed by the decision processor, the priority given a particular emission processor result by the decision processor, etc. In any case, the scaling may be dynamic or static. Also, the weights  552 - 568  may be eliminated explicitly or implicitly be setting the values of the weights  552 - 568  all equal to one. 
     A first example audio processor system  600  that may be used to implement any or all of the audio code detector  312 , the audio signature processor  316 , the audio gain level processor  320 , the horizontal sync audio processor  324 , the quiet time detector  328  and/or the fan noise processor  332  of  FIG.  3    is shown in  FIG.  6   . The example audio processor system  600  is configured to process audio signals emanating from the monitored display device  120  (or, more generally, a corresponding information presenting device) and detected by the audio sensor  204 . The audio processor system  600  includes an analog-to-digital (A/D) converter  604  to sample the audio signal  230  output by the audio sensor  204  and convert the audio signal  230  to a digital format for processing by the processor  612 . The audio processor system  600  also includes a variable gain amplifier (VGA)  616  which may amplify or attenuate, as needed, the audio signal  230  so that the audio signal  230  appropriately fills the dynamic range of the A/D converter  604  to yield a desired bit resolution at the output of the A/D converter  604 . 
     The processor  612  may be configured to control the gain/attenuation provided by the VGA  616  based on any known automatic gain control (AGC) algorithm. For example, an AGC algorithm implemented by the processor  612  may control the VGA  616  to yield an output of the A/D converter  604  having an amplitude, variance, standard deviation, energy, etc. within a predetermined range. The predetermined range is typically derived from the characteristics of the particular A/D converter  604  to result in a gain/attenuation of the VGA  616  that appropriately fills the dynamic range of the A/D converter  604 . 
     In addition to implementing the AGC algorithm, the processor  612  may also be configured to execute machine readable instructions to implement one or more of the audio code detector  312 , the audio signature processor  316 , the audio gain level processor  320 , the horizontal sync audio processor  324 , the quiet time detector  328  and/or the fan noise processor  332 . Such machine readable instructions are discussed in greater detail below in connection with  FIGS.  13 - 19   . 
     A second example audio processor system  700  that may be used to implement any or all of the audio code detector  312 , the audio signature processor  316 , the audio gain level processor  320 , the horizontal sync audio processor  324 , the quiet time detector  328 , the fan noise processor  332  and/or the audio source detector  336  of  FIG.  3    is shown in  FIG.  7   . The example audio processor system  700  is configured to process audio signals emanating from the monitored display device  120  (or, more generally, a corresponding information presenting device) and detected by two or more audio sensors  204 A-B. The audio processor system  700  includes a first A/D converter  704 A to sample the audio signal  230 A output by the audio sensor  204 A and convert the audio signal  230 A to a digital format for processing by the processor  712 . The audio processor system  700  also includes a first VGA  716 A which may amplify or attenuate, as needed, the audio signal  230 A so that the audio signal  230 A appropriately fills the dynamic range of the A/D converter  604 A to yield a desired bit resolution at the output of the A/D converter  604 A. 
     The audio processor system  700  also includes a second A/D converter  704 B to sample the audio signal  230 B output by the audio sensor  204 B and convert the audio signal  230 B to a digital format for processing by the processor  712 . Additionally, the audio processor system  700  includes a second VGA  716 B which may amplify or attenuate, as needed, the audio signal  230 B so that the audio signal  230 B appropriately fills the dynamic range of the A/D converter  704 B to yield a desired bit resolution at the output of the A/D converter  704 B. 
     The processor  712  may be configured to control the gain/attenuation provided by the VGAs  716 A-B based on any known AGC algorithm as discussed above in connection with  FIG.  6   . In addition to implementing the AGC algorithm, the processor  712  may also be configured to execute machine readable instructions to implement one or more of the audio code detector  312 , the audio signature processor  316 , the audio gain level processor  320 , the horizontal sync audio processor  324 , the quiet time detector  328 , the fan noise processor  332  and/or the audio source detector  336 . Such machine readable instructions are discussed in greater detail below in connection with  FIGS.  13 - 20   . 
     An example video processor system  800  that may be used to implement any or all of the visible light rhythm processor  412  and/or the display activity detector  416  of  FIG.  4    is shown in  FIG.  8   . The example video processor system  800  is configured to process video signals corresponding to the display of the monitored display device  120  (or, more generally, a corresponding information presenting device) as detected by the video sensor  208 . The video processor system  800  includes a frame grabber  804  to capture video frames corresponding to video signal  234  output by the video sensor  208  for processing by the processor  812 . Any known technique for capturing video frames and storing such video frames in a digital format may be used to implement the frame grabber  804 . 
     The processor  812  may be configured to execute machine readable instructions to implement one or more of the visible light rhythm processor  412  and/or the display activity detector  416 . Such machine readable instructions are discussed in greater detail below in connection with  FIGS.  21 - 22   . 
     An example EM field processor system  900  that may be used to implement the EM field detector  512  of  FIG.  5    is shown in  FIGS.  9 A-B . The example EM field processor system  900  is configured to process EM field emissions corresponding to the monitored display device  120  (or, more generally, a corresponding information presenting device) as detected by an emission sensor  212  implemented alternatively as an inductive or capacitive pickup  212  in  FIG.  9 A  or as an antenna pickup  212  in  FIG.  9 B . In the examples of  FIGS.  9 A- 9 B , the emission sensor  212  provides the EM field signal  532  shown in  FIG.  5    for processing by the EM field processor system  900 . Inductive, capacitive and antenna pickups for detecting EM fields are known and, as such, are not discussed further herein. 
     The EM field processor system  900  includes an A/D converter  904  to sample the EM field signal  532  output by the emission sensor  212  and convert the EM field signal  532  to a digital format for processing by the processor  912 . The processor  912  may be configured to execute machine readable instructions to implement the EM field detector  512 . Such machine readable instructions are discussed in greater detail below in connection with  FIG.  23   . 
     An example current measurement processor system  1000  that may be used to implement the current detector  516  of  FIG.  5    is shown in  FIG.  10   . The example current measurement processor system  1000  is configured to measure the amount of current drawn by the monitored display device  120  (or, more generally, a corresponding information presenting device) from a power source  1002 . The current draw is detected by an emission sensor  212  implemented, for example, as a current sense transformer  212  coupled between the monitored display device  120  and the power source  1002  as shown. In the example of  FIG.  10   , the emission sensor  212  provides the current measurement signal  536  shown in  FIG.  5    for processing by the current measurement processor system  1000 . Current sense transformers for measuring current draw are known and, as such, are not discussed further herein. 
     The current measurement processor system  1000  includes an A/D converter  1004  to sample the current measurement signal  536  output by the emission sensor  212  and convert the current measurement signal  536  to a digital format for processing by the processor  1012 . The processor  1012  may be configured to execute machine readable instructions to implement the current detector  516 . Such machine readable instructions are discussed in greater detail below in connection with  FIG.  24   . 
     An example temperature processor system  1100  that may be used to implement the temperature detector  520  of  FIG.  5    is shown in  FIG.  11   . The example temperature processor system  1100  is configured to measure heat emanating from the monitored display device  120  (or, more generally, a corresponding information presenting device). The heat emanating from the monitored display device  120  is detected by an emission sensor  212 A implemented, for example, as a temperature sensor  212 A coupled or positioned proximate to the monitored display device  120  as shown. In the example of  FIG.  11   , the emission sensor  212 A provides a first temperature signal  540 A, similar to the temperature signal  540  shown in  FIG.  5   , for processing by the temperature processor system  1100 . 
     The temperature processor system  1100  may also include a second emission sensor  212 B implemented, for example, as a temperature sensor  212 B. The second emission sensor  212 B may positioned to measure, for example, the ambient temperature of the room in which the monitored display device  120  is located. In the example of  FIG.  11   , the emission sensor  212 B provides a second temperature signal  540 B, similar to the temperature signal  540  shown in  FIG.  5   , for processing by the temperature processor system  1100 . The temperature sensors  212 A-B may be implemented by, for example, thermistors, analog silicon temperature sensors and/or digital silicon temperature sensors, all of which are known and, as such, are not discussed further herein. 
     The temperature processor system  1100  includes a first A/D converter  1104 A to sample the temperature signal  540 A output by the emission sensor  212 A and convert the temperature signal  540 A to a digital format for processing by the processor  1112 . The temperature processor system  1100  also includes a second A/D converter  1104 B to sample the temperature signal  540 B output by the emission sensor  212 B and convert the audio signal  540 B to a digital format for processing by the processor  1112 . The processor  1112  may be configured to execute machine readable instructions to implement the temperature detector  520 . Such machine readable instructions are discussed in greater detail below in connection with  FIG.  25   . 
     Three example remote device activity processor systems  1200 ,  1250  any  1280 , any or all of which may be used to implement the remote control activity detector  524  and/or the people meter activity detector  528  of  FIG.  5   , are shown in  FIGS.  12 A,  12 B and  12 C , respectively. The example remote device activity processor systems  1200 ,  1250  and  1280  are configured to measure control signals transmitted by the remote control device  160  and/or by the people meter control device  164  used in conjunction with the monitored display device  120 . In the first example remote device activity processor system  1200 , the control signals are detected by an emission sensor  212  implemented, for example, as an infrared (IR) detector  212  for scenarios in which either or both of the remote control device  160  and/or the people meter control device  164  employ IR signal transmission. In the second example remote device activity processor system  1250 , the control signals are detected by an emission sensor  212  implemented, for example, as an antenna  212  for scenarios in which either or both of the remote control device  160  and/or the people meter control device  164  employ RF signal transmission. In the third example remote device activity processor system  1280 , the control signals are detected by an emission sensor  212  implemented, for example, as an ultrasonic transducer  212  for scenarios in which either or both of the remote control device  160  and/or the people meter control device  164  employ ultrasonic signal transmission. IR detectors, antennas and ultrasonic transducers are known and, as such, are not discussed further herein. 
     The first example remote device activity processor system  1200  includes an IR receiver  1204  to receive IR signals detected by the IR detector  212 . The IR receiver  1204  generates corresponding received control signals from the IR signals and outputs the received control signals for processing by the processor  1212 . The second example remote device activity processor system  1250  includes a wireless receiver  1254  to receive RF signals detected by the antenna  212 . The wireless receiver  1254  generates corresponding received control signals from the RF signals and outputs the received control signals for processing by the processor  1212 . The third example remote device activity processor system  1280  includes an ultrasonic receiver  1284  to receive ultrasonic signals detected by the ultrasonic transducer  212 . The ultrasonic receiver  1284  generates corresponding received control signals from the ultrasonic signals and outputs the received control signals for processing by the processor  1292 . The processors  1212 ,  1262  and  1292  may be configured to execute machine readable instructions to implement the remote control activity detector  524  and/or the people meter activity detector  528 . Such machine readable instructions are discussed in greater detail below in connection with  FIG.  26   . 
     Flowcharts representative of example machine readable instructions that may be executed to implement the audio processors  228  of  FIG.  3   , the video processors  232  of  FIG.  4   , the emission processors  236  of  FIG.  5    and/or the decision processor  244  of  FIG.  2    are shown in  FIG.  13  through  28   . In these examples, the machine readable instructions represented by each flowchart may comprise one or more programs for execution by: (a) a processor, such as the processors  612 ,  712 ,  812 ,  912 ,  1012 ,  1112 ,  1212 ,  1262  and/or  1292 , or the processor  2912  shown in the example computer  2900  discussed below in connection with  FIG.  29   , (b) a controller, and/or (c) any other suitable device. The one or more programs may be embodied in software stored on a tangible medium such as, for example, a flash memory, a CD-ROM, a floppy disk, a hard drive, a DVD, or a memory associated with the processors  612 ,  712 ,  812 ,  912 ,  1012 ,  1112 ,  1212 ,  1262 ,  1292  and/or  2912 , but persons of ordinary skill in the art will readily appreciate that the entire program or programs and/or portions thereof could alternatively be executed by a device other than the processors  612 ,  712 ,  812 ,  912 ,  1012 ,  1112 ,  1212 ,  1262 ,  1292  and/or  2912  and/or embodied in firmware or dedicated hardware in a well-known manner (e.g., implemented by an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable logic device (FPLD), discrete logic, etc.). For example, any or all of the audio processors  228 , the video processors  232 , the emission processors  236  and/or the decision processor  244  could be implemented by any combination of software, hardware, and/or firmware. Also, some or all of the machine readable instructions represented by the flowchart of  FIGS.  13  through  28    may be implemented manually. Further, although the example machine readable instructions are described with reference to the flowcharts illustrated in  FIGS.  13  through  28   , persons of ordinary skill in the art will readily appreciate that many other techniques for implementing the example methods and apparatus described herein may alternatively be used. For example, with reference to the flowcharts illustrated in  FIGS.  13  through  28   , the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, combined and/or subdivided into multiple blocks. 
     Example machine readable instructions  1300  that may be executed to implement the audio code detector  312  of  FIG.  3    are shown in  FIG.  13   . The machine readable instructions  1300  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the audio code detector  312 . The machine readable instructions  1300  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1300  begin execution at block  1304  at which the audio code detector  312  performs an automatic gain control (AGC) algorithm which causes a variable gain amplifier (VGA) (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the audio code detector  312 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. An example AGC algorithm implemented by the audio code detector  312  may control the VGA to yield an output of the A/D converter having an amplitude, variance, standard deviation, energy, etc. within a predetermined range. The predetermined range is based on the characteristics of the particular A/D converter and targeted to achieve an appropriate filling of the A/D converter&#39;s dynamic range. AGC algorithms are known in the art and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1304 , control proceeds to block  1308  at which the audio code detector  312  checks for audio codes present in the received audio signal. Any appropriate technique for decoding audio codes embedded in a content presentation may be used, such as one or more of those discussed above in connection with the description of  FIG.  3   . If at block  1312  the audio code detector  312  detects the presence of a valid audio code, control proceeds to block  1316  at which the audio code detector  312  determines the monitored information presenting device is ON. The audio code detector  312  makes such a determination because the presence of the valid audio code indicates that the monitored information presenting device is emitting an audio signal corresponding to presented program content. If, however, at block  1312  the audio code detector  312  does not detect the presence of a valid audio code, control proceeds to block  1320  at which the audio code detector  312  determines the monitored information presenting device is probably OFF. Here, the audio code detector  312  uses the lack of a valid code to decide that the monitored information presenting device is not emitting an audio signal corresponding to presented program content and, therefore, is probably turned OFF (although the device could be operating in an audio mute state). In any case, after the audio code detector  312  makes a determination at block  1316  or block  1320 , execution of the machine readable instructions  1300  ends. 
     First example machine readable instructions  1400  that may be executed to implement the audio signature processor  316  of  FIG.  3    are shown in  FIG.  14   . The machine readable instructions  1400  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the audio signature processor  316 . The machine readable instructions  1400  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1400  begin execution at block  1404  at which the audio signature processor  316  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the audio signature processor  316 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1404 , control proceeds to block  1408  at which the audio signature processor  316  generates an audio signature from the received audio signal. Any appropriate technique for generating audio signatures based on an audio signal corresponding to a content presentation may be used, such as one or more of those discussed above in connection with the description of  FIG.  3   . If at block  1412  the audio signature processor  316  determines that the audio signature generates at block  1408  matches a known reference signature, control proceeds to block  1416  at which the audio signature processor  316  determines that the monitored information presenting device is ON. The audio signature processor  316  makes such a determination because the signature match indicates that the monitored information presenting device is, at least, emitting an audio signal corresponding to presented program content corresponding to the reference audio signature. If, however, at block  1412  the audio signature processor  316  does not detect a match, control proceeds to block  1420  at which the audio signature processor  316  determines that the monitored information presenting device is probably OFF. Here, the audio signature processor  316  uses the lack of a match to decide that the monitored information presenting device is not emitting an audio signal corresponding to presented program content and, therefore, is probably turned OFF (although the lack of a match could also correspond to an audio mute state, unknown program content, etc.). In any case, after audio signature processor  316  makes a determination at block  1416  or block  1420 , execution of the machine readable instructions  1400  ends. 
     Second example machine readable instructions  1500  that may be executed to implement the audio signature processor  316  of  FIG.  3    are shown in  FIG.  15   . The machine readable instructions  1500  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the audio signature processor  316 . The machine readable instructions  1500  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1500  begin execution at block  1504  at which the audio signature processor  316  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the audio signature processor  316 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1504 , control proceeds to block  1508  at which the audio signature processor  316  generates an audio signature from the received audio signal. Any appropriate technique for generating audio signatures based on an audio signal corresponding to a content presentation may be used, such as one or more of those discussed above in connection with the description of  FIG.  3   . 
     Control then proceeds to block  1512  at which the audio signature processor  316  determines whether the audio signature generates at block  1508  may be characterized as “hissy.” Typically, an audio signal corresponding to audible program content exhibits significant peak energy fluctuations caused by the varying pressure wave associated with the audio emissions. Conversely, an audio signal corresponding to background noise or silence exhibits relatively small peak energy fluctuations about an average energy value resulting in sound typically characterized as “hissy.” Thus, the audio signature processor  316  may evaluate whether the audio signature generated at block  1508  is hissy to determine whether a monitored information presenting device is emitting an audio signal corresponding to audible program content. In an example hissy audio signature detection algorithm, the audio signature processor  316  may compute a running average of peak energy values of the audio signal. Then, if a particular peak energy value is within some region about this running average, the audio signature processor  316  may determine that a possible hissy state has been entered. If such a possible hissy state exists for a period of time (e.g., three seconds), the audio signature processor  316  may decide that a definite hissy state has been entered and declare the generated audio signature to be hissy. Persons of ordinary skill in the art will appreciate that many techniques may be used to determine whether an audio signature is hissy or, in other words, corresponds to silence or background noise. For example, the average time between audio energy peaks or the variability of the standard deviation of the audio energy peaks may be used to determine whether the audio signal energy fluctuates sufficiently to indicate the presence of an audio content presentation or is relatively static and, therefore, indicative of silence or background noise. 
     Returning to  FIG.  15   , if at block  1512  the audio signature processor  316  determines that the audio signature generated at block  1408  is hissy, control proceeds to block  1516  at which the audio signature processor  316  determines that the monitored information presenting device is OFF. The audio signature processor  316  makes such a determination because a hissy signature indicates that the received audio signal corresponds most likely to background noise and not audio emanating from the monitored information presenting device, thereby indicating that the information presenting device is OFF. If, however, at block  1512  the audio signature processor  316  determines that the generated audio signature is not hissy, control proceeds to block  1520  at which the audio signature processor  316  determines that the monitored information presenting device is probably ON. Here, the audio signature processor  316  uses the lack of a hissyness to decide that the monitored information presenting device is probably emitting an audio signal corresponding to presented program content and, therefore, is probably turned ON. In any case, after audio signature processor  316  makes a determination at block  1516  or block  1520 , execution of the machine readable instructions  1500  ends. 
     Example machine readable instructions  1600  that may be executed to implement the audio gain level processor  320  of  FIG.  3    are shown in  FIG.  16   . The machine readable instructions  1600  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the audio gain level processor  320 . The machine readable instructions  1600  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1600  begin execution at block  1604  at which the audio gain level processor  320  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the audio gain level processor  320 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1604 , control proceeds to block  1608  at which the audio gain level processor  320  examines the steady-state audio gain level to which the AGC algorithm converged at block  1604 . In particular, the audio gain level processor  320  determines whether the steady-state audio gain level exceeds a predetermined threshold indicative of the AGC algorithm converging to a large, possibly maximum, gain. Such a large/maximum convergence would occur of the input audio signal corresponded to silence or background noise. If at block  1612  the audio gain level processor  320  determines that the steady-state audio gain level achieved at block  1604  does not exceed the predetermined threshold, control proceeds to block  1616  at which the audio gain level processor  320  determines that the monitored information presenting device is probably ON. The audio gain level processor  320  makes such a determination because the steady-state gain level indicates that an audio signal emitted from the monitored information presenting device was probably detected and provided as input to the audio gain level processor  320 . If, however, at block  1612  the steady-state audio gain level exceeds the threshold, control proceeds to block  1620  at which audio gain level processor  320  determines that the monitored information presenting device is probably OFF. Here, the audio gain level processor  320  uses the large/maximum steady-state audio gain to decide that the monitored information presenting device is probably not emitting an audio signal corresponding to presented program content and, therefore, is probably turned OFF. In any case, after audio gain level processor  320  makes a determination at block  1616  or block  1620 , execution of the machine readable instructions  1600  ends. 
     Example machine readable instructions  1700  that may be executed to implement the horizontal sync audio processor  324  of  FIG.  3    are shown in  FIG.  17   . The machine readable instructions  1700  process audio noise signals emitted by, for example, a horizontal scan fly-back transformer of an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the horizontal sync audio processor  324 . The machine readable instructions  1700  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1700  begin execution at block  1704  at which the horizontal sync audio processor  324  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the horizontal sync audio processor  324 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1704 , control proceeds to block  1708  at which the horizontal sync audio processor  324  examines the frequency spectrum of the input audio signal for characteristics corresponding to audio emitted by a fly-back transformer. For example, and as discussed above in connection with  FIG.  3   , a fly-back transformer used in an information presenting device operating in accordance with the NTSC standard may generate tonal audio emissions having a frequency of approximately 15.75 kHz. Therefore, if at block  1712  the horizontal sync audio processor  324  detects the presence of audio frequency tones indicative of a fly-back transformer, control proceeds to block  1716  at which the horizontal sync audio processor  324  determines the monitored information presenting device is ON. The horizontal sync audio processor  324  makes such a determination because the presence of audio emissions corresponding to a fly-back transformer indicates that the monitored information presenting device is operating in an active state. If, however, at block  1712  the horizontal sync audio processor  324  does not detect the presence of audio frequency tones indicative of a fly-back transformer, control proceeds to block  1720  at which the horizontal sync audio processor  324  determines the monitored information presenting device is probably OFF. Here, the horizontal sync audio processor  324  uses the lack of audio emissions corresponding to a fly-back transformer to decide that the monitored information presenting device is probably not operating and, therefore, is probably turned OFF. In any case, after the horizontal sync audio processor  324  makes a determination at block  1716  or block  1720 , execution of the machine readable instructions  1700  ends. 
     Example machine readable instructions  1800  that may be executed to implement the quiet time detector  328  of  FIG.  3    are shown in  FIG.  18   . The machine readable instructions  1800  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the audio gain level processor  320 . The machine readable instructions  1800  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1800  begin execution at block  1804  at which the quiet time detector  328  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the quiet time detector  328 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1804 , control proceeds to block  1808  at which the quiet time detector  328  performs a quiet time detector algorithm to determine whether the audio signal includes any periods of silence indicative of, for example, a channel change operation, a transition between broadcast program content and a commercial, etc. Any appropriate technique for detecting intervals of quiet time based on an audio signal corresponding to a content presentation may be used, such as the technique discussed above in connection with the description of  FIG.  3   . If at block  1812  the quiet time detector  328  determines that a quiet time interval was detected at block  1808 , control proceeds to block  1816  at which the quiet time detector  328  determines that the monitored information presenting device is probably ON. The quiet time detector  328  makes such a determination because the audio signal emitted from the monitored information presenting device includes quiet time intervals probably indicative of short interruptions of program content presented by an actively-operating information presenting device. 
     If, however, at block  1812  a quiet time interval is not detected, control proceeds to block  1820  at which the quiet time detector  328  determines whether a quiet time interval was detected within a predetermined preceding interval of time. If at block  1820  the quiet time detector  328  determines that a quiet time interval was detected within the preceding interval of time, control proceeds to block  1816  at which the quiet time detector  328  determines that the monitored information presenting device is probably ON. The quiet time detector  328  makes such a determination because the audio signal emitted from the monitored information presenting device recently included quiet time intervals probably indicative of short interruptions of program content presented by an actively-operating information presenting device. If, however, at block  1820  the quiet time detector  328  determines that a quiet time interval was also not detected within the predetermined preceding interval of time, control proceeds to block  1828  at which the quiet time detector  328  determines that the monitored information presenting device is probably OFF. Here, the quiet time detector  328  uses the lack of a quiet time interval within the predetermined period of time to decide that the monitored information presenting device is probably not emitting an audio signal corresponding to presented program content and, therefore, is probably turned OFF. In any case, after quiet time detector  328  makes a determination at block  1816  or block  1828 , execution of the machine readable instructions  1800  ends. 
     Example machine readable instructions  1900  that may be executed to implement the fan noise detector  332  of  FIG.  3    are shown in  FIG.  19   . The machine readable instructions  1900  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an audio sensor (e.g., the audio sensor  204  of  FIGS.  2  and  6   ) and input to the fan noise detector  332 . The machine readable instructions  1900  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  1900  begin execution at block  1904  at which the fan noise detector  332  performs an AGC algorithm which causes a VGA (e.g., the VGA  616  of  FIG.  6   ) to amplify or attenuate the audio signal (e.g., the audio signal  230  of  FIGS.  2  and  6   ) applied to the input of the fan noise detector  332 . The audio signal is amplified/attenuated to appropriately fill the dynamic range of an A/D converter (e.g., the A/D converter  604  of  FIG.  6   ) used to sample and convert the audio signal to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithm at block  1904 , control proceeds to block  1908  at which the fan noise detector  332  checks for the presence of fan noise in the received audio signal. Fan noise from an operating information presenting device typically exhibits tonal energy in the frequency range between 300 Hz and 5 kHz. As such, any known technique for detecting tonal audio signals in this (or any other appropriate) frequency range may be used at block  1908 . If at block  1912  the fan noise detector  332  detects the presence of fan noise, control proceeds to block  1916  at which the fan noise detector  332  determines the monitored information presenting device is probably ON. The fan noise detector  332  makes such a determination because the presence of fan noise indicates that the monitored information presenting device is probably operating and presenting program content. If, however, at block  1912  the fan noise detector  332  does not detect the presence of fan noise, control proceeds to block  1920  at which the fan noise detector  332  determines the monitored information presenting device is probably OFF. Here, the fan noise detector  332  uses the lack of fan noise to decide that the monitored information presenting device is probably not operating and, therefore, is probably turned OFF. In any case, after the fan noise detector  332  makes a determination at block  1916  or block  1920 , execution of the machine readable instructions  1900  ends. 
     Example machine readable instructions  2000  that may be executed to implement the audio source detector  336  of  FIG.  3    are shown in  FIG.  20   . The machine readable instructions  2000  process audio signals emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by audio sensors (e.g., the audio sensors  204 A-B of  FIG.  7   ) and input to the audio source detector  336 . The machine readable instructions  20000  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  2000  begin execution at block  2004  at which the audio source detector  336  performs AGC algorithms which cause VGAs (e.g., the VGAs  716 A-B of  FIG.  7   ) to amplify or attenuate audio signals (e.g., the audio signals  230 A-B of  FIG.  7   ) applied to the inputs of the audio source detector  336 . The audio signals are amplified/attenuated to appropriately fill the dynamic range of A/D converters (e.g., the A/D converters  704 A-B of  FIG.  7   ) used to sample and convert the audio signals to a digital format for further processing. AGC algorithms are discussed in greater detail above in connection with  FIG.  13    and, as such, are not discussed further herein. 
     After convergence of the AGC algorithms at block  2004 , control proceeds to block  2008  at which the audio source detector  336  performs a source detection algorithm to determine the source of the input audio signals. Any appropriate technique for audio source detection may be used, such as one or more of those discussed above in connection with the description of  FIG.  3   . Next, if at block  2012  the audio source detector  336  determines that the audio source location coincides with the location of the monitored information presenting device, control proceeds to block  2016  at which the audio source detector  336  determines the monitored information presenting device is probably ON. The audio source detector  336  makes such a determination because the audio source detection algorithm performed at block  2008  detected audio probably emanating from the monitored information presenting device and corresponding to presented program content. If, however, at block  2012  the location of the detected audio source does not correspond with the monitored information presenting device, control proceeds to block  2020  at which the audio source detector  336  determines the monitored information presenting device is probably OFF. Here, the audio source detector  336  decides the input audio signal probably does not correspond to the monitored information presenting device and, thus, the information presenting device is probably OFF. In any case, after the audio source detector  336  makes a determination at block  2016  or block  2020 , execution of the machine readable instructions  2000  ends. 
     Example machine readable instructions  2100  that may be executed to implement the visible light rhythm processor  412  of  FIG.  4    are shown in  FIG.  21   . The machine readable instructions  2100  process visible light emitted by the display of an information presenting device (e.g., the display device  120  of  FIG.  1   ). The emitted light is detected by a video sensor (e.g., the video sensor  208  of  FIGS.  2  and  8   ) positioned to monitor the display of the monitored information presenting device (hereinafter referred to as the monitored display). The video sensor converts the emitted light to an electrical signal which is input to the visible light rhythm processor  412 . The machine readable instructions  2100  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. 
     The machine readable instructions  2100  begin execution at block  2104  at which the visible light rhythm processor  412  determines the intensity of the light detected by the video sensor by sampling the signal provided by the video sensor. Next, control proceeds to block  2108  at which the visible light rhythm processor  412  examines the light intensities, for example, over a predetermined interval of time. If at block  2112  the visible light rhythm processor  412  determines that the light intensities indicate that the monitored display is active, control proceeds to block  2116  at which the visible light rhythm processor  412  determines that the monitored information presenting device is probably ON. The visible light rhythm processor  412  makes such a determination, for example, by comparing the light intensities to a predetermined threshold corresponding to a light intensity visible to the human eye and, therefore, probably indicative of the information presenting device displaying active program content. If, however, at block  2112  the visible light rhythm processor  412  determines that the light intensities do not indicate that the monitored display is active, control proceeds to block  2120  at which the visible light rhythm processor  412  determines that the monitored information presenting device is probably OFF. Here, the lack of detected light intensities which would be visible to the human eye probably indicates that the monitored information presenting device is inactive and, therefore, probably turned OFF. In any case, after the visible light rhythm processor  412  makes a determination at block  2116  or block  2120 , execution of the machine readable instructions  2100  ends. 
     Example machine readable instructions  2200  that may be executed to implement the display activity detector  416  of  FIG.  4    are shown in  FIG.  22   . The machine readable instructions  2200  process video images corresponding to an area including the display of an information presenting device (e.g., the display device  120  of  FIG.  1   ). The video images are detected by a video sensor (e.g., the video sensor  208  of  FIGS.  2  and  8   ) and input to the display activity detector  416 . The video sensor is positioned to monitor an area including the display of the monitored information presenting device (hereinafter referred to as the monitored display). The machine readable instructions  2200  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. 
     The machine readable instructions  2200  begin execution at block  2204  at which the display activity detector  416  captures video frames based on the video signal (e.g., the video signal  234  of  FIGS.  2  and  8   ) applied to the input of the display activity detector  416 . As discussed above, the display activity detector  416  may use a frame grabber (e.g., the frame grabber  804  of  FIG.  8   ) to capture the video frames. After the video frames are captured at  2204 , control proceeds to block  2208  at which the display activity detector  416  locates the monitored display in the captured video frames. Control then proceeds to block  2212  at which the display activity detector  416  extracts one or more regions corresponding to the monitored display from each captured video frame. Then, at block  2216 , the display activity detector  416  compares the extracted regions between successive video frames to determine whether the regions differ. For example, the display activity detector  416  may compute a distance metric between the same regions in successive video frames. Then, if the distance metric exceeds a predetermined threshold, the display activity detector  416  may determine that a change has occurred in the region over time. 
     Returning to  FIG.  22   , if at block  2220  the display activity detector  416  detects that the extracted regions differ between successive video frames, control proceeds to block  2224  at which the display activity detector  416  determines the monitored information presenting device is ON. The display activity detector  416  makes such a determination because the change in the extracted regions indicate that the monitored display is displaying a changing video presentation and, thus, that the monitored information presenting device is ON. If, however, at block  2220  the display activity detector  416  does not detect a difference between the extracted regions, control proceeds to block  2228  at which the display activity detector  416  determines the monitored information presenting device is probably OFF. Here, the display activity detector  416  uses the lack of a change in the extracted regions to decide that the monitored display is not displaying a changing video presentation and, therefore, the monitored information presenting device is probably turned OFF. 
     The display activity detector  416  may be configured to increase the confidence of the OFF decision by examining, for example, the color of the extracted region. If the color of the extracted region is a uniform dark color (e.g., black), the display activity detector  416  may determine that the monitored display is more likely turned OFF than, for example, displaying a paused video image. In any case, after the display activity detector  416  makes a determination at block  2224  or block  2228 , execution of the machine readable instructions  2200  ends. 
     Example machine readable instructions  2300  that may be executed to implement the electromagnetic (EM) field detector  512  of  FIG.  5    are shown in  FIG.  23   . The machine readable instructions  2300  process an EM field signal corresponding to an EM field emitted by an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an emission sensor (e.g., the emission sensor  212  of  FIGS.  2  and  9 A -B) and input to the EM field detector  512 . The machine readable instructions  2300  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  2300  begin execution at block  2304  at which the EM field detector  512  samples the input EM field signal. After sampling the input EM field signal, control proceeds to block  2308  at which the EM field detector  512  compares the sampled EM field signal to a predetermined threshold determined, for example, by a calibration procedure which measures the background EM field in an area surrounding the monitored information presenting device. 
     If at block  2308  the EM field detector  512  determines that the sampled EM field signal exceeds the threshold, control proceeds to block  2312  at which the EM field detector  512  determines the monitored information presenting device is ON. The EM field detector  512  makes such a determination because the presence of an EM field exceeding the predetermined threshold indicates that the monitored information presenting device is turned ON and operating in an active mode. If, however, at block  2308  the EM field detector  512  determines that the EM field signal does not exceed the threshold, control proceeds to block  2316  at which the EM field detector  512  determines the monitored information presenting device is OFF. Here, the EM field detector  512  uses the lack of a significant EM field to decide that the monitored information presenting device is not operating in an active mode and, therefore, is turned OFF. In any case, after the EM field detector  512  makes a determination at block  2312  or block  2316 , execution of the machine readable instructions  2300  ends. 
     Example machine readable instructions  2400  that may be executed to implement the current detector  516  of  FIG.  5    are shown in  FIG.  24   . The machine readable instructions  2400  process a measured current signal corresponding to current drawn from a power source coupled to an information presenting device (e.g., the display device  120  of  FIG.  1   ), detected by an emission sensor (e.g., the emission sensor  212  of  FIGS.  2  and  10   ) and input to the current detector  516 . The machine readable instructions  2400  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  2400  begin execution at block  2404  at which the current detector  516  samples the input current signal. After sampling the input current signal, control proceeds to block  2408  at which the current detector  516  compares the sampled current signal to a predetermined threshold determined, for example, my measuring the amount of current drawn by the monitored information presenting device in an OFF or standby/sleep mode. 
     If at block  2408  the current detector  516  determines that the sampled current signal exceeds the threshold, control proceeds to block  2412  at which the current detector  516  determines the monitored information presenting device is ON. The current detector  516  makes such a determination because a current signal exceeding the predetermined threshold indicates that the monitored information presenting device is turned ON and drawing current from the associated power source. If, however, at block  2408  the current detector  516  determines that the current signal does not exceed the threshold, control proceeds to block  2416  at which the current detector  516  determines the monitored information presenting device is OFF. Here, the current detector  516  uses the lack of a significant current signal to decide that the monitored information presenting device is not operating in an active mode and, therefore, is turned OFF. In any case, after the current detector  516  makes a determination at block  2412  or block  2416 , execution of the machine readable instructions  2400  ends. 
     Example machine readable instructions  2500  that may be executed to implement the temperature detector  520  of  FIG.  5    are shown in  FIG.  25   . The machine readable instructions  2500  process measured temperature measurements corresponding to heat emitted from an information presenting device (e.g., the display device  120  of  FIG.  1   ), as well as possibly the ambient air temperature in a room in which the monitored information presenting device is located. The temperature measurements are detected by appropriately configured emission sensors (e.g., the emission sensors  212 A-B of  FIG.  11   ) and input to the temperature detector  516 . The machine readable instructions  2500  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. The machine readable instructions  2500  begin execution at block  2504  at which the temperature detector  520  samples the temperature signal generated by a first emission sensor positioned to permit measurement of the temperature of the monitored information presenting device. Next, control proceeds to block  2508  at which the temperature detector  520  samples the temperature signal generated by a second emission sensor positioned to permit measurement of the ambient air temperature. 
     After sampling of the respective temperature signals, control then proceeds to block  2512  at which the temperature detector  520  compares the monitored information presenting device&#39;s temperature to the ambient air temperature, possible offset by a threshold to improve ON/OFF detection reliability. If at block  2512  the temperature detector  520  determines that the monitored information presenting device&#39;s temperature sufficiently exceeds the ambient air temperature (based on the additional threshold amount), control proceeds to block  2516  at which the temperature detector  520  determines that the monitored information presenting device is ON. The temperature detector  520  makes such a determination because the monitored information presenting device&#39;s temperature indicates that heat is being emitted and, thus, that the device is turned ON. If, however, at block  2512  monitored information presenting device&#39;s temperature does not sufficiently exceed the ambient air temperature, control proceeds to block  2520  at which the temperature detector  520  determines the monitored information presenting device is OFF. Here, the temperature detector  520  uses the lack of a significant heat emission to decide that the monitored information presenting device is not operating in an active mode and, therefore, is turned OFF. In any case, after the temperature detector  520  makes a determination at block  2516  or block  2520 , execution of the machine readable instructions  2500  ends. Persons of ordinary skill in the art will appreciate that the processing at step  2508  may be eliminated to reduce the number of required emission sensors if, for example, the threshold at block  2512  is modified to incorporate an expected/average ambient air temperature. 
     Example machine readable instructions  2600  that may be executed to implement the remote control activity detector  524  and/or the people meter activity detector  528  of  FIG.  5    are shown in  FIG.  26   . To simplify the description of  FIG.  26   , the remote control activity detector  524  and the people meter activity detector  528  will be referred to generally and collectively as the “remote input device activity detector  524 / 528 .” The machine readable instructions  2600  process control signals emitted by one or more remote input devices (e.g., the remote control device  160  and/or the people meter control device  164  of  FIG.  1   ) associated with an information presenting device (e.g., the display device  120  of  FIG.  1   ). The control signals are detected by appropriately configured emission sensors (e.g., the emission sensors  212  of  FIG.  12 A-B ) and input to the remote input device activity detector  524 / 528 . The machine readable instructions  2600  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether the monitored information presenting device is ON or OFF. 
     The machine readable instructions  2600  begin execution at block  2604  at which the remote input device activity detector  524 / 528  initializes/configures a receiver (e.g., the IR receiver  1204  of  FIG.  12 A , the wireless receiver  1254  of  FIG.  12 B  and/or the ultrasonic receiver  1284  of  FIG.  12 C ) which receives and transforms the control signals detected by the emission sensor into a form suitable for subsequent processing by the remote input device activity detector  524 / 528 . After the receiver is appropriately configured, control proceeds to block  2608  at which the remote input device activity detector  524 / 528  processes the received control signals. If at block  2612  the remote input device activity detector  524 / 528  determines that the received control signals correspond to known and/or unknown remote input device activity, control proceeds to block  2616  at which the remote input device activity detector  524 / 528  determines that the monitored information presenting device is probably ON. For example, known activity could include power ON commands, channel change commands, volume change/mute commands, prompt responses, etc., whereas unknown activity could include a noticeable increase in IR, RF or ultrasonic energy, a cluster of received IR, RF or ultrasonic pulses, etc. The remote input device activity detector  524 / 528  makes such a determination at block  2616  because the receipt of control signals corresponding to known and/or unknown remote input device activity indicates that a user is probably operating and/or responding to an active information presenting device. 
     If, however, at block  2612  control signals corresponding to known and/or unknown remote input device activity are not detected, control proceeds to block  2620  at which the remote input device activity detector  524 / 528  determines the monitored information presenting device is probably OFF. Here, the remote input device activity detector  524 / 528  uses the lack of received control signals corresponding to known and/or unknown remote input device activity to decide that the monitored information presenting device is not being controlled and/or responded to by a user and, therefore, is probably turned OFF. In any case, after the remote input device activity detector  524 / 528  makes a determination at block  2616  or block  2620 , execution of the machine readable instructions  2600  ends. 
     Example machine readable instructions  2700  that may be executed to implement the decision processor  244  of  FIG.  2    are shown in  FIG.  27   . The machine readable instructions  2700  may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether a monitored information presenting device (e.g., the display device  120  of  FIG.  1   ) is ON or OFF. The machine readable instructions  2700  process, for example, the ON/OFF decision outputs  246 ,  248  and/or  250  generated by the audio processors  228 , the video processors  232  and the emission processors  236 , respectively, of  FIG.  2   . The individual audio processors  228 , the video processors  232  and the emission processors  236  make autonomous decisions concerning whether a monitored information presenting device is turned ON or OFF. The machine readable instructions  2700  enable the decision processor  244  to combine the individual, autonomous ON/OFF decisions into a single, comprehensive decision regarding whether the monitored information presenting device is turned ON or OFF. 
     The machine readable instructions  2700  begin execution at block  2704  at which the decision processor  244  samples the audio decision outputs  246  (also called audio decision metrics  246 ) generated by the audio processors  228 . Next, control proceeds to block  2708  at which the decision processor  244  samples the video decision outputs  248  (also called video decision metrics  248 ) generated by the video processors  232 . Control then proceeds to block  2712  at which the decision processor  244  samples the emission decision outputs  250  (also called emission decision metrics  250 ) generated by the emission processors  236 . Then, after all the decision metrics have been sampled, control proceeds to block  2716  at which the decision processor  244  weights the decision metrics by, for example, scaling or assigning a value to each decision metric corresponding to the confidence associated with the decision metric. For example, and referring to the examples of  FIGS.  13 - 26    above, at block  2716  the decision processor  244  may assign a value of +1 to decision metric of “ON,” a value of +0.5 to a decision metric of “probably ON,” a value of −0.5 to a decision metric of “probably OFF” and a value of −1 to a decision metric of “OFF.” 
     Next, control proceeds to block  2720  at which the decision processor  244  combines all of the individual decision metrics (e.g., via addition) to determine a weighted majority vote of the individual decisions made by the audio processors  228 , the video processors  232  and the emission processors  236 . Then, if at block  2724  the majority vote favors a decision that the monitored information presenting device is ON (e.g., if the weighted majority vote results in a positive value), control proceeds to block  2728  at which the decision processor  244  declares the monitored information presenting device to be ON. However, if at block  2724  the majority vote favors a decision that the monitored information presenting device is OFF (e.g., if the majority vote results in a negative value), control proceeds to block  2732  at which the decision processor  244  declares the monitored information presenting device to be OFF. In the case of a tie, the decision processor  244  may be configured, for example, to favor either a decision of ON or OFF depending on the particular monitored information presenting device, to produce an output indicating that the state of the monitored information presenting device is indeterminate, etc. In any case, after the decision processor  244  makes a determination at block  2728  or block  2732 , execution of the machine readable instructions  2700  ends. 
       FIG.  28    illustrates second example machine readable instructions  2800  that may be executed to implement the decision processor  244  of  FIG.  2   . As in the case of the example machine readable instructions  2700  of  FIG.  27   , the machine readable instructions  2800  of  FIG.  28    may be executed periodically (e.g., as part of a program loop) and/or aperiodically (e.g., in response to one or more events) to determine whether a monitored information presenting device (e.g., the display device  120  of  FIG.  1   ) is ON or OFF. Furthermore, the machine readable instructions  2800  similarly process, for example, the ON/OFF decision outputs  246 ,  248  and/or  250  generated by the audio processors  228 , the video processors  232  and the emission processors  236 , respectively, of  FIG.  2   . As such, blocks having substantially equivalent functionality in the examples of  FIGS.  27  and  28    are labeled with the same reference numeral. The interested reader is referred to the description of  FIG.  27    above for a detailed description of these blocks. 
     Turning to the example of  FIG.  28   , the example machine readable instructions  2800  implement a two-stage weighted majority voting procedure, in contrast with the single-stage voting procedure implemented by the example machine readable instructions  2700  of  FIG.  27   . Specifically, after sampling the audio decision metrics  246  at block  2704 , control proceeds to block  2806  at which the decision processor  244  computes a weighted majority vote of the audio decision metrics. The audio metric weighted majority vote may be computed at block  2806 , for example, by scaling or assigning a value to each sampled audio decision metric  246  and then adding the resulting metrics to determine the audio metric weighted majority vote. Similarly, a video metric weighted majority vote and an emission metric weighted majority vote may be computed at blocks  2810  and  2814 , respectively, after the corresponding video decision metrics and emission decision metrics are sampled at blocks  2708  and  2712  as shown. 
     Next, after processing at blocks  2806 ,  2810  and  2812  completes, control proceeds to block  2818  at which the decision processor  244  may further weight the individual audio, video and emission metric weighted majority votes based on, for example, the confidence and/or importance associated with the particular type of metric. Control then proceeds to block  2822  at which the decision processor  244  combines the resulting individual audio, video and emission metric weighted majority votes to determine an overall majority vote. Then, control proceeds to block  2724  and blocks subsequent thereto as discussed above in connection with  FIG.  27    at which the decision processor  244  uses the overall weighted majority vote to decide whether the monitored information presenting device is turned ON or OFF. Execution of the machine readable instructions  2800  then ends. 
     Persons of ordinary skill in the art will appreciate that the examples of  FIGS.  27  and  28    are but two techniques contemplated by the disclosure herein for combining the ON/OFF decision outputs  246 ,  248  and/or  250  generated by, respectively, the audio processors  228 , the video processors  232  and the emission processors  236 . As another example, the decision processor  244  could combine the ON/OFF decision outputs  246 ,  248  and/or  250  based on whether a particular decision output corresponds to a presentation by the monitored information presenting device or whether the decision output corresponds to a physical operation of the information presenting device. In such an example, a first weighted majority vote corresponding to the presentation by the monitored information presenting device could be computed from, for example, the decision outputs from any or all of the audio code detector  312 , the audio signature processor  316 , the audio gain level processor  320 , the quiet time detector  332 , the audio source detector  336 , the visible light rhythm processor  412  and/or the display activity detector  416 . A second weighted majority vote corresponding to the physical operation of the monitored information presenting device could be computed from, for example, the decision outputs from any or all of the horizontal sync audio processor  324 , the fan noise detector  332 , the EM field detector  512 , the current detector  516 , the temperature detector  520 , the remote control activity detector  524  and/or the people meter activity detector  528 . Then, the first and second weighted majority votes could be combined to generate an overall majority vote to determine whether the monitored information presenting device is turned ON or OFF. 
       FIG.  29    is a block diagram of an example computer  2900  capable of implementing the apparatus and methods disclosed herein. The computer  2900  can be, for example, a server, a personal computer, a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a personal video recorder, a set top box, or any other type of computing device. 
     The system  2900  of the instant example includes a processor  2912  such as a general purpose programmable processor. The processor  2912  includes a local memory  2914 , and executes coded instructions  2916  present in the local memory  2914  and/or in another memory device. The processor  2912  may execute, among other things, the machine readable instructions represented in  FIGS.  13  through  28    and/or implement any or all of the processors  612 ,  712 ,  812 ,  912 ,  1012 ,  1112 ,  1212 ,  1262  and/or  1292 . The processor  2912  may be any type of processing unit, such as one or more microprocessor from the Intel® Centrino® family of microprocessors, the Intel® Pentium® family of microprocessors, the Intel® Itanium® family of microprocessors, and/or the Intel XScale® family of processors. Of course, other processors from other families are also appropriate. 
     The processor  2912  is in communication with a main memory including a volatile memory  2918  and a non-volatile memory  2920  via a bus  2922 . The volatile memory  2918  may be implemented by Static Random Access Memory (SRAM), Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any other type of random access memory device. The non-volatile memory  2920  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  2918 ,  2920  is typically controlled by a memory controller (not shown) in a conventional manner. 
     The computer  2900  also includes a conventional interface circuit  2924 . The interface circuit  2924  may be implemented by any type of well known interface standard, such as an Ethernet interface, a universal serial bus (USB), and/or a third generation input/output (3GIO) interface. 
     One or more input devices  2926  are connected to the interface circuit  2924 . The input device(s)  2926  permit a user to enter data and commands into the processor  2912 . The input device(s) can be implemented by, for example, a keyboard, a mouse, a touchscreen, a track-pad, a trackball, an isopoint and/or a voice recognition system. 
     One or more output devices  2928  are also connected to the interface circuit  2924 . The output devices  2928  can be implemented, for example, by display devices (e.g., a liquid crystal display, a cathode ray tube display (CRT)), by a printer and/or by speakers. The interface circuit  2924 , thus, typically includes a graphics driver card. 
     The interface circuit  2924  also includes a communication device such as a modem or network interface card to facilitate exchange of data with external computers via a network (e.g., an Ethernet connection, a digital subscriber line (DSL), a telephone line, coaxial cable, a cellular telephone system, etc.). 
     The computer  2900  also includes one or more mass storage devices  2930  for storing software and data. Examples of such mass storage devices  2930  include floppy disk drives, hard drive disks, compact disk drives and digital versatile disk (DVD) drives. The mass storage device  2930  may be used, for example, store any or all of the machine readable instructions  1300 ,  1400 ,  1500 ,  1600 ,  1700 ,  1800 ,  1900 ,  2000 ,  2100 ,  2200 ,  2300 ,  2400 ,  2500 ,  2600 ,  2700  and/or  2800 . Additionally, the volatile memory  1518  may be used, for example, to store any or all of the audio decision metrics  246 , the video decision metrics  248  and/or the emission decision metrics  250 . 
     At least some of the above described example methods and/or apparatus are implemented by one or more software and/or firmware programs running on a computer processor. However, dedicated hardware implementations including, but not limited to, application specific integrated circuits (ASICs), programmable logic arrays (PLAs) and other hardware devices can likewise be constructed to implement some or all of the example methods and/or apparatus described herein, either in whole or in part. Furthermore, alternative software implementations including, but not limited to, distributed processing or component/object distributed processing, parallel processing, or virtual machine processing can also be constructed to implement the example methods and/or apparatus described herein. 
     It should also be noted that the example software and/or firmware implementations described herein are optionally stored on a tangible storage medium, such as: a magnetic medium (e.g., a magnetic disk or tape); a magneto-optical or optical medium such as an optical disk; or a solid state medium such as a memory card or other package that houses one or more read-only (non-volatile) memories, random access memories, or other re-writable (volatile) memories; or a signal containing computer instructions. A digital file attached to e-mail or other information archive or set of archives is considered a distribution medium equivalent to a tangible storage medium. Accordingly, the example software and/or firmware described herein can be stored on a tangible storage medium or distribution medium such as those described above or successor storage media. 
     Additionally, although this patent discloses example systems including software or firmware executed on hardware, it should be noted that such systems are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of these hardware and software components could be embodied exclusively in hardware, exclusively in software, exclusively in firmware or in some combination of hardware, firmware and/or software. Accordingly, while the above specification described example systems, methods and articles of manufacture, persons of ordinary skill in the art will readily appreciate that the examples are not the only way to implement such systems, methods and articles of manufacture. Therefore, although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.