The present invention relates to a patient monitoring system, and more particularly to a pressure sensitive pad that sounds an alarm when weight is removed from it.  There are many individuals who are physically challenged that are confined to beds or wheelchairs because of illness, disability, or age.  Many of these people require assistance in living, but typically they cannot be continuously monitored throughout the day and night.  If a patient attempts to leave a bed or chair, or falls out of a bed or chair, they may lie unconscious for a period of time endangering their health and life.  To aid in the care of these individuals, medical safety devices have been developed that sound an alarm when a person falls or wanders off against the wishes of the caregiver.  The noise produced by these safety devices alerts nurses or other aid personnel that the patient is in need of assistance. 
There are a variety of prior art devices that are used to monitor patients.  In one type of system, one end of a cord is securely attached to a patient with the other end of the cord being attached to an alarm system.  When the patient moves beyond the length of the cord, the cord is pulled free from the alarm system.  This causes an audible alarm to be given.  This type of system is disclosed in U.S. Pat.  Nos.  4,577,185; 4,583,084; and 6,239,704. 
Another prior art device for monitoring patients comprises a pressurized fluid that is contained in members that are attached to the side rails of a bed.  When a patient attempts to gets out of bed, the patient will typically grasp the side rails, which activates an alarm.  However, this device does not provide a warning when a patient falls out of bed involuntarily, or when the bed is not provided with suitable side rails. 
There have also been a number of pressure sensitive pads disclosed in prior art.  One such pad is Feldl (U.S. Pat.  No.  4,020,482).  Feldl teaches a flexible bag that is placed below a mattress of a bed in a hospital or nursing home.  When weight is removed from the bag, pressure in the bag is lost and a switch is activated, giving a signal at the attendant's station.  The problem with this type of device is that it may be difficult to set the pressure in the bag correctly.  Different mattresses and different patients weigh different amounts, and thus if the bag pressure is not set correctly, the alarm may be given at the wrong times, or not given at the proper times. 
There is therefore a need for a pressure sensitive pad that can produce a warning to caregivers when a patient moves from a chair or bed either voluntarily or involuntarily.