Out-of-range personnel monitor and alarm

An out-of-range alarm system for generating an alarm whenever a mobile unit in the system extends beyond a prescribed limit from a base unit, said alarm system comprising;

• a fixed base unit having therein a transmitter for generating an omnidirectional output signal at a first frequency, said output signal emanating from a single source point, a receiver for detecting a signal at a second frequency, and an alarm associated with said receiver for producing an alarm signal upon the detection of said second frequency signal;
• and
• at least one mobile unit having a receiver for detecting said first frequency signal transmitted by said base unit, threshold circuitry coupled to said receiver for generating a threshold output signal upon a failure of said mobile unit receiver to detect said first signal at a predetermined signal strength, and a transmitter coupled to said threshold circuitry for generating an output signal at said second frequency in response to said threshold output signal.