Melnor AquaSentry Automatic Rain Delay... Stop watering your lawn or garden when Mother Nature is already doing the job. The AquaSentry, in conjunction with select Melnor AquaTimers, tests soil before watering assuring healthier plants and beautiful lawns, while conserving precious resources. Requires two AA batteries. 3300 AquaSentry works with current model AquaTimers 3015, 3060, 3100, and 3280.