Short range radio pulse transmitter design?
The transmitter will output a pulse every few seconds, transmit a small burst at X frequency. The receiver then outputs a short high pulse/outputs high for the duration of the received pulse.
I want this to be as simple as it can possibly be, cost being the primary restriction and power usage being also of fairly high importance, so please no suggestions of Bluetooth or xbee type systems.
It does not have to be a radio based system, however it needs to work without line of sight and of course without connecting wires.
If it helps the overall aim is a 'safety signal' that will set of an alarm at the receiving end if several pulses are missed
EDIT: To clarify I am looking for simple, like really simple. So the transmitter is just a resonator and antenna. What I need is a simple receiver that will respond to a specific frequency, on or off. Does such a thing exist?