First we recommend lowering the sensor to about 2 – 3 feet of the ground. Also, make sure all transmitter dip switches (there’s 10 of them) inside the sensor are set to “0” or “Off” and match the switches inside the chime/receiever (there’s 8 switches in the receiver). Don’t forget, anytime you make any change to the sensor or chime you’ll need to reset the unit by removing the power, waiting 30 seconds the replacing the power (either the battery, or plugging it back in).

Also, the infra red system works by detecting moving heat, so cold vehicles etc. which have not had a chance to warm up yet will not set the sensor off.
These instructions are helpful for the Dakota Alert WMA-3000 and the Dakota Alert DCMA-2500.