Have used them for several years. Alarms reliably at the end of a 400 foot driveway. Three items worth mentioning: 1. Deer, squirrels, crows etc. will set off the alarm regardless of the senitivity selection. 2. The audible alarm is IMO too weak, even on the full volume setting. 3. There is no provision to attach a separate alarm method (such as a light or external siren.