Entry Sensor Error

Flashing blue light on base station. Sensor error #XXX on keypad. Removed sensor & replaced battery, old 3.0v, new 3.2v. Worked for a week and same problem. Checked battery okay. Re-seated battery. Worked for a few days then same problem. Checked battery okay. Re-seated battery. Working for now.
When sensor is removed keypad indicates open sensor as it should. What gives?