A method of operating a vehicle locating unit wherein an activation signal is received when the vehicle is stolen and in response to the activation signal, a signal indicating the vehicle has been stolen is transmitted. The receiver is energized for an actual duration Non periodically to listen for the activation and other signals. Estimating how long the receiver has been on includes incrementing a counter at a count resolution where Non is typically at least sometimes less than the count resolution. Estimating the total amount of time the receiver was energized is based on a measured on time after it converges with the actual on time.