Also got this...
We have ~1/4 mile gravel driveway winding up through the woods to our house. Got this alarm w/ 4 sensors. Spaced the sensors along the driveway with the closest one close to the house. Linked each sensor to a different channel on the receiver, and gave each channel a different alarm tone. So when a car, or person, comes up the driveway, we hear the different tones go off in succession.
When a deer walks by, we hear the tone for that zone, but if the tones don't progress in succession, we know it's not somebody coming up the driveway.
Have had it for about a month now, and works great. Sensors have a good range, and I put them on trees back in the woods a bit from the driveway. So even if you know they're there, you would have a very hard time seeing them. I did get the range extender just to be sure. Put it near an upstairs window for better line-of-sight to all the sensors. Put the receiver on the TV cabinet right under the TV. So we not only hear the alarms, we see the LEDs light for the zone that was tripped.
This thing is pretty cool.