ComfortCall has a small attachment that plugs into the bottom of any Venstar Slimline thermostat that makes all this possible. ComfortCall will tell the caller what the inside and outside temperatures are, the status of the thermostat (if the heating or cooling is currently on or off), and will let user to adjust the thermostat to its pre-set comfort settings or energy saving settings or turn the system off. This is all done via voice or keypad entry from any telephone.
In addition to the small attachment on the thermostat, ComfortCall has a small wireless base station, about the size of a deck of cards, which connects directly to the telephone line or answering machine. It is fully compatible with answering machines via a command that sends the call to the ComfortCall thermostat attachment and hangs up the answering machine.
ComfortCall is also compatible with the X10 home automation system so users can also use the device to turn on and off the lights that are configured into the system. As well, when the user turns the thermostat to energy saving settings, it will turn off the designated lights. Built-in security codes ensure that only authorized users may access ComfortCall.
More information: http://www.venstar.com/Thermostats/