This garage monitor sensor is awesome. It beeps loudly every 5 minutes when garage is open and covers a range of 150-300 feet between transmitter and receiver depending on interference. It has the option of turning on or off the 5 minute beeping thing if you know your garage is open and don't want to hear the beep. The manual says the sensor requires a CR2032 type battery when the one i bought came with a CR2025 battery. i guess either works fine. I believe the further your sensor is from your receiver, the harder the battery works. The sensor battery's voltage really makes a difference in its accurate reading and check the battery's voltage every once in a while to make sure it stays above 3 volts and not more than .1 volts less because that is when the receiver starts acting all funny by beeping closed and open constantly. The battery is about 5 dollars, but it is worth it every month or so to be aware of your garage's security.

I love this item. Have had it for two years. My garage door was left open all night lots of times because I forgot it was open. Now the sentry tells me when the door is open. It works really good. I consider it a "must have" for folks with attached garages where they can't see their garage doors to know if they are open or not. Have also given this as a gift and everyone we give it to loves it.

With 2 teenage boys who use the garage door as the main entry in the house, I now know when they get home and that the door was closed behind them. Great product, easy to install.

This item is not dependable. I needed a device that worked as this one is described however after numerous false readings over 2 days it became clear that this item is not effective. Save you money and manually check to see if the door is open, this item is sure to disappoint.

Seems like a simple enough device, but the unit shipped to me simply does not work. I played with it for a half hour going thoroughly through the instruction manual, checking the battery voltages, etc, but the transmitter would never register with the receiver. Oh well, buyer beware.