The first thing we always recommend is changing the battery. Even if it’s a brand new battery, we’d recommend changing it for another new one OR if you have a volt meter make sure it’s measuring 9V or higher. It’s amazing the number of ‘new’ batteries sold which are already low, directly from the store.
If that doesn’t solve it, the next step in trouble shooting is to bring the sensor inside and place it in an area like a closet, facing the wall where nothing will be moving in front of it activating the alarm. If this stops the false alarms then there is something happening outside which is setting off your Optex driveway alarm.
If the false alarms continue, and the battery is reading 9V or higher, as a last step remove the battery from the Optex TD-20U sensor. If the alarms stop, then yes something has gone wrong with the TD-20U and it is false alarming. If the alarms continue, then we know that for some reason your RC-20U is actually false alarming on it’s own, in which the Optex RC-20U is the component that needs to be replaced.
You can view and purchase all Optex 2000 equipment here – http://www.absoluteautomation.com/rctd20u-optex-wireless-2000/