The ELK M1XRF319 uses a 319.5 MHz frequency and the ELK M1XRFWM uses Spread Spectrum Frequency hopping 902 – 928 MHz. Open Air Line of Sight testing the range for both is fairly close at approximately 300-500 feet. The true test of a wireless sensor depends on the environment and the construction material (wood, sheetrock, stone, rebar, concrete, metal duct work and so on). With the ELK Two-way (M1XRFTWM and 6000 Series of sensors) the sensors have a status feedback LED that lets you know the signal was received. When the senor is tripped if the LED turns Green the signal was acknowledged/received but if the LED turns Red the sensor is either out of range of the M1XRFTWM or the sensor is not learned into the system.