The thermostat is used as any other one, but with the added facility of choosing the day or night temperature setting by means of a telephone. The remote control facility is operated via the telephone keypad, thus a DTMF type phone is required. From audio signals sent down the line, the user receives a report back on how the thermostat is set. Switching is protected by a security code, set by the user, which is keyed into the telephone in a simple manner.

Specifications: separate settings for day/night temp. with LED indication, relay output with LED indication 5A / 240V AC (1200W), telephone pick-up after ± 3 or 8 rings, report when the temperature has fallen below 37.4°F, automatic hang-up if no code is received within 40 secs., possible security codes from 000 to 999, day temperature from 57°F to 79°F, night temperature setting from 43°F to 64°F, hysteresis (allowed temperature swing) 0.1°F, local manual control & supply voltage 110V AC