what type of field does 508d emit

Does anyone know the field that 508D emit to detect objects? I read some that says radar field in the product, while others say it's ultrasonic. In the manual it just says ultra high frequency field.

Microwave, very low power, I believe 44GHz but I'm not sure of the frequency, detects the water in the human body but therefore also susceptible to rain water false alarms.

Thanks for the info. I'll check the interference of that and some other radio waves. I'm trying to figure out what's causing false alarms that seem to have happened after I move the antenna along with some wires of the 5902 close to the sensor ... On another somewhat related question, does anyone know if I can remove the casing for the 508D sensor and it would still work? I assume I have to keep the sheet of aluminum on the bottom.

Yes it will still work and yes you will still need a ground plane. The diagnostics will tell you what triggered it.