14 the crc sequence is provided for error detection and is well known in the art see for example w stallings data and computer communications 101 110 1985 which is hereby incorporated by reference in addition since the supervisory message is being transmitted the transmission power control signal 52 transitions to a high state that is then used to control the transmission power established in the rf amplifier modulator function 40 conversely if a non supervisory message an alarm message is being generated in response to a change in the status of one or more alarm sensor inputs 50 then the transmission power control 52 signal would maintain or transition to a low state which will cause the rf amplifier modulator function 40 to transmit the non supervisory message at the predetermined normal or maximum power level prior to outputting the generated message the message generation function 36 will enable the phase locked loop function 38 using a pll enable signal 54 conceptually phase locked loop circuits utilize feedback to maintain an output signal in a specific phase relationship to a reference signal here the phase locked loop function 38 serves to maintain the phase difference between the oscillator function 34 and the signal that is modulated by the message data signal 76 the modulated signal of vco output signal 70 is typically between 417 mhz and 433 mhz the phase locked loop function 38 is comprised of a voltage controlled oscillator vco 58 a loop filter 60 a phase detector 62 and a divider 64 the phase detector 62 comprises a device that produces an output voltage proportional to the phase difference between an phase detection clock 66 and a divider output signal 68 the vco 58 is a circuit that produces a.