A friend put me on to these and they are great. I have purchase 3 of them from walmart and they are battery operated by 3 D cells. My friend purchase just one about six months ago for his front prouch to let his cat in and out during the night and the batteries are still going strong. The reason I am write this is I have 12 acres of land and wooded and they work great on trees and I also have some on trees coming up my long driveway. I did put industral strenght batteries in the ones I have.