in a deep sleep at 1 am this morning when the obnoxious chirping started. Sounded like the house was full of huge crickets. Out to the garage to get a ladder and obviously the single one on the ground floor wasn't the culprit. Had to drag the ladder upstairs, but was lucky in that the highest one in the master bedroom was the first one I tried and it was the culprit. I usually change all the batteries yearly, but this time it was early. Time to shorten the replace span. I may even take a couple off the grid to make it easier to find the bad one in the future.