Passive infrared/acoustic pool security system

A pool security system incorporates a passive infrared element and an underwater acoustic element. The passive infrared detection element generates a thin infrared layer which overlays the entire water surface area of the pool. As a heat generating body passes through the infrared layer, the infrared element detects the body and generates a first detect signal. As the body enters the water, it causes waves which propagate through the water. These waves are detected by the acoustic element. The acoustic element continues to receive waves generated as the body struggles at or below the water surface. A master control circuit is coupled to the infrared and the acoustic elements to receive the first and second detect signals. The master control circuit is designed to detect when the first detect signal is received, followed a predetermined time by the second detect signal. When this occurs, the master control circuit will generate an alarm signal, thus alerting others of the danger of unauthorized entry.

BACKGROUND OF THE INVENTION 
This invention relates generally to security alarm systems, and more 
specifically, to security alarm systems for swimming pools and other 
contained bodies of liquid. 
The number of drowning incidents in private swimming pools in the United 
States has reached tragic proportions in recent years. Drowning is 
particularly prevalent among young children who do not know how to swim, 
or are not capable of getting out of pools under emergency or accidental 
situations. Statistics show that about 3 to 5 children drown in private 
swimming pools each day. 
Alarm systems designed for pools generally fall within three categories. 
The first category includes sensors activated by surface wave motion. 
Surface sensors comprise elements such as floatation devices. A major 
problem with floatation devices is the devices can be activated by wind or 
inanimate objects falling into the pool. Furthermore, floatation devices 
may be accidentally triggered by pool cleaning systems. 
A second category includes hydrophones which detects splashing noises. A 
significant problem associated with hydrophones is that hydrophones can be 
activated with loud or low flying aircraft. 
The third major category includes transducers secured below the pool's 
water surface. The transducers are activated when an object falling into 
the pool creates wave motions which propagate through the water. A problem 
with transducers, as with the other types of conventional security 
systems, is the sensor cannot distinguish a child from an inanimate 
object. 
Attempts have been made to combine transducers, or the other types of 
conventional security systems, with other sensing devices. These have met 
with limited to poor success as evidenced by the lack of reliable pool 
security systems to date. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a pool 
security system which distinguishes animate objects from inanimate objects 
that fall into pools. 
Another object of the present invention is to provide a pool security 
system which incorporates a passive infrared element and an acoustic 
element to substantially decrease the occurrence of false alarms. 
To achieve the above objects of the present invention, a pool security 
system is disclosed which incorporates a passive infrared element and an 
underwater acoustic element. The passive infrared element generates a thin 
infrared layer which overlays the entire water surface area of the pool. 
As a heat generating body passes through the infrared layer, the infrared 
element detects the body due to changes in heat and generates a first 
detect signal. As the body enters the water, it causes waves which 
propagate through the water. These waves are detected by the acoustic 
element. The acoustic element continues to detect the waves generated as 
the body struggles at or below the water and the acoustic element 
generates a second detect signal. A master control circuit is coupled to 
the infrared and the acoustic elements to receive the first and second 
detect signals. The master control circuit is designed to detect when the 
first detect signal is received, followed a predetermined time by the 
second detect signal. When this occurs, the master control circuit will 
generate an alarm signal, thus alerting others of the danger of 
unauthorized entry. 
These and other objects of the present invention will become apparent from 
the following detailed description of the invention when considered in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a pool 8 is shown having an infrared/acoustic pool 
security system 10 that sounds an alarm when a child, pet, or other 
animate body has entered the pool uninvited or fallen into the pool 
accidentally. Infrared/acoustic pool security system 10 comprises infrared 
element 12, acoustic element 14, control circuit 16, and alarm mechanism 
18. 
Infrared element 12 creates a passive infrared detection layer 22 above the 
water surface 24 of pool 8. Infrared element 12 is secured to the edge of 
pool 8 a predetermined height above water surface 24. Positioning infrared 
element 12 above water surface 24 prevents wave action of water surface 24 
from interfering or communicating with passive infrared detection layer 
22. In its preferred embodiment, infrared element 12 is also positioned 
below deck 15 of pool 8. With infrared element 12 positioned below deck 15 
passive infrared detection layer 22 is confined within the area of the 
pool as defined by deck 15. 
FIG. 2 shows a front view of infrared element 12 comprising a narrow, 
elongated lens 26. Elongated lens 26 reaches horizontally across the front 
of infrared element 12. Infrared element 12 is secured to pool 8 of FIG. 1 
such that an axis of the length of elongated lens 26 is generally parallel 
with water surface 24. Elongated lens 26 is sealed within water-proof 
housing 28 of infrared element 12. 
Accuracy during installation of infrared element 12 is necessary for the 
proper orientation of passive infrared detection layer 22. Referring again 
to FIG. 1, infrared element 12 must be installed so that passive infrared 
blanket 22 is horizontal with water surface 24. A deviation of 
approximately six inches from horizontal over a span of sixty feet is 
considered a reasonable tolerance. 
Elongated lens 26 of FIG. 2 can be constructed to radiate passive infrared 
detection layer 22 over a spectrum of 180 degrees horizontal as shown in 
FIG. 3. However, many pools are not circular or rectangular. A single 
infrared element 12 cannot radiate passive infrared detection layer 22 
over the entire surface area of water surface 24. Various blind spots 
would occur. To alleviate the blind spots, more than one infrared element 
12 may be incorporated. Each infrared element 12 would be secured to pool 
8 in a particular location, depending upon the shape of pool 8, to cover 
the entire surface area of water surface 2. Positioning two infrared 
elements 12 across the peanut shaped pool 8 of FIG. 3 eliminates blind 
spots of passive infrared detection layer 22. 
Infrared element 12 may be secured to the top of deck 15. This positioning 
of infrared element 12 allows passive infrared detection layer 22 to cover 
a much larger area. The positioning further prevents elongated lens 26 
from becoming spotted from water splashing on infrared element 12. 
However, allowing passive infrared detection 22 layer to radiate unbounded 
increases the probability of false alarms of infrared/acoustic pool 
security system 10. For instance, a cat passing across deck 15 could 
activate infrared element 12. Therefore, infrared element 12 is preferably 
positioned such that passive infrared detection layer 22 is bounded by 
deck 15. By positioning infrared element 12 high enough up the side of 
pool 8, yet below deck 15, contact of elongated lens 26 of FIG. 2 with 
water from pool 8 can be substantially reduced. Furthermore, elongated 
lens 26 may be chemically treated to prevent water spotting. Frequent 
visual inspection and cleaning of elongated lens 26 can also avoid spot 
interference with passive infrared detection layer 22. 
Infrared element 12 detects a heat emitting body as it passes through 
passive detection layer 22. In fact, infrared element 12 may be designed 
to detect changes of heat within a single heat emitting body as the body 
passes through passive infrared detection layer 22. Therefore, when an 
animate body passes through passive infrared detection layer 22, infrared 
element 12 detects the change in heat due to the body and generates an 
infrared detect signal. 
Acoustic element 14 preferably comprises a transducer secured underneath 
water surface 24 of pool 8. Acoustic element 14 detects wave motions 
propagating through the water of pool 8. Since air movement at water 
surface 24 can generate wave motions through the water, acoustic element 
14 can be adjusted to detect wave motions of predetermined magnitudes. 
Acoustic element 14 can also be positioned within pool 8 to detect 
specific wave propagation such as vertical rather than horizontal waves. 
Acoustic element 14 can further be adjusted to distinguish waves generated 
by pool cleaning systems from waves generated by a struggling child. 
When an animate body enters pool 8, acoustic element 14 detects wave 
propagation generated by the animate body, and generates an acoustic 
detect signal. 
It should be understood that various types of transducers may be used for 
acoustic element 14. For instance, underwater microphones may be utilized 
as well as more advanced, specially designed transducers. 
Infrared element 12 and acoustic element 14 are coupled to control circuit 
16. The infrared detect signal from infrared element 12, and the acoustic 
detect signal from acoustic element 14 are relayed to control circuit 16. 
In the preferred embodiment, control circuit 16 generates an alarm when 
the infrared and acoustic detect signals are receive by control circuit 16 
in a predetermined sequence. 
When a child falls into pool 8, the child will first pass through passive 
infrared detection layer 22. The infrared detect signal is generated and 
relayed to control circuit 16. The child then enters the water and begins 
to struggle. Acoustic element 14 detects the waves propagated through the 
water and generates the acoustic detect signal. The acoustic detect signal 
is then relayed to control circuit 16. If the acoustic detect signal is 
receive by control circuit 16 a predetermined time after infrared detect 
signal is received by control circuit 16, an alarm is generated. The alarm 
is illustrated by alarm 18 of FIG. 1. 
Combining infrared element 12 and acoustic element 14 substantially reduces 
false alarms. For instance, if only acoustic element 14 is used, any 
number of inanimate objects falling into pool 8 would cause alarm 18 to be 
activated. Similarly, infrared element 12, by itself, could cause far more 
false alarms than the combination of infrared element 12 and acoustic 
element 14 with the timing of control circuit 16. However, use of infrared 
element 12 by itself would result in fewer false alarms than use of 
acoustic element 14 by itself. 
Thus, there has been described a passive infrared/acoustic pool security 
system which meets all the objects, aims, and advantages of the present 
invention. Although the invention has been specifically described in terms 
of specific embodiments, other alternatives, variations, and modifications 
are embraced within the spirit and broad scope of the appended claims.