US Patent 7239047 Switch device incorporating capacitive oscillator

A switch (10) comprises a face plate (16) and a single switch sensing oscillator (18) responsive to a switch activating presence. The oscillator (18) has a resistive component (36) connected to a sensing plate (38) which acts as a first capacitor plate. The face plate (16) is arranged to prevent electrical contact between the user and the oscillator (18). Any object, when placed adjacent the face plate (16), acts as a second capacitor plate which alters the frequency of the oscillator (18). A microprocessor (20) senses the smoke detector (62). In a further aspect the switch includes a mains electricity cable signal transmitter/receiver and a microprocessor whereby each such switch may communicate directly with another such switch.