Combating the rapid increase in the theft of air conditioner (A/C) units for the precious metals they contain, a low-cost device from AC Watchdog protects A/Cs through multiple alarm options triggered by tampering. The key to the affordabilty, according to inventor Joseph Wojtowicz, is the use of a customized pressure sensor that directly monitors the pressure of the A/C’s refrigerant.

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According to Wojtowicz, an HVAC technician, the device aims primarily to protect victims of this theft who cannot afford to replace their A/Cs. The device also has the potential to reduce insurance premiums and preclude the need for expensive security surveillance.

Wojtowicz states the pressure sensor is based on a resistance-changing element. Though the part was custom designed for the AC Watchdog device, its unique configuration reduces the total cost of the system. The patent for the technology is pending, and replications of the technology based on off-the-shelf sensors will probably not have the same cost advantage, according to Wojtowicz.

The most effective alarm mode for the system has proven to be conventional dialing to a predefined number, in addition to the audio alarm that sounds at the facility when the device detects tampering with the A/C. Other options, such as battery backup, interfacing to exisiting security-system trigger channels, and wireless notification are also available. However, the wireless option introduces additional expenses and is not anticipated to be the first choice of the target clients for the device.

"I saw their frustration when they [A/C theft victims] realized they had to replace their A/C unit with a new one. Many people cannot afford to replace an expensive item such as this on a whim. Some are elderly people, families with children, people who must have an air conditioner at all times during hot weather," states Wojtowicz.

Wojtowicz, motivated by the frequency of such experiences with A/C-theft victims, constructed the first working prototype in his garage. He then optimized the analog circuit design with the low-cost custom resistive pressure sensor.

Given the recent heat wave that has afflicted much of the continental United States, this technology indirectly provides the additional capability of protecting those who are particularly vulnerable to hot weather. Wojtowicz is working with HVAC contractors and technicians around the United States to be able to provide AC Watchdog protection to everyone. The unit must be installed by a technician, so Wojtowicz is using online resources as an outreach method to find dependable contractors in every area.

More information is available at the AC Watchdog Web site.