How many times have all of us been somewhere, idling away the time, when the smell of smoke enters the room. The moment the smoke is smelled, long-forgotten events come back, and lets us know that the okra is now a charred mess. This is highly undesirable, as no one likes to have the meal that they have slaved over for so long, be burned by a few moments of inattention. Furthermore, this constitutes a significant fire hazard, as the okra may even start burning after a while.
An especially acute problem results when the stove is unattended for a very long period of time. For instance, a user may actually leave his premises while the stove is still on. This could present a significant fire hazard, especially if the user leaves for a very long period.
Typically sensing devices sense the presence of a user by sensing heat. This heat sensor is actuated whenever a temperature change occurs within the area which it covers. Such temperature change will occur whenever a moving object, most notably a person, passes within its range. However, other external stimuli may "fool" this device into thinking a user is within its area, and may in fact turn on the device.
The prior art has dealt with the problems due to user inattendance in relatively ineffective ways. One such way is discussed in U.S. Pat. No. 4,346,427 to Blissett et al. This patent shows an automatic control device in which a sensor detects the presence or absence of an individual within a service area. The presence of an individual causes a control device to be energized. When the individual leaves the service area, a time delay causes the device to remain energized for a predetermined period. After this period, the device is automatically deactivated. The return of the individual to the service area re-energizes the control device.
This patent teaches that such a system might be used to control interior lighting or room air conditioners. When the individual leaves the control area in Blissett, the device control is turned off. When the individual once again enters the location of the sensor, the device is turned on. There is no overriding shutoff in Blissett to deal with the user having left for too long a period.
U.S. Pat. No. 3,670,167 to Forbes teaches an automatic sensing arrangement which activates plumbing fixtures upon detection of the presence of an individual. However, this patent also does not teach an overriding shutoff system that will permanently shut off the device.
U.S. Pat. Nos. 4,029,176; 4,031,408; and 4,433,328 all teach motion sensing switches, activated when a person enters a field area. U.S. Pat. Nos. 3,958,118; 3,858,192; 4,179,691; 4,375,034; and 4,377,808 all relate to intrusion sensing systems. However, none of these patents provide any teaching which would lead to the advantages that are obtained by the present invention.