Sorry, I though the entire code was unnecessary. Now I have inserted the entire code. I have checked on the serial monitor, false trigger has not occurred at least for 1-2 hours of testing. The offset value don't change even after few days. I have a feeling that it has something to do with the global variable AdjOffsetFlag , but I am only guessing. I assume that use of software serial AltSoftSerial in the program couldn't have overflow the stack use too. I same issue persist even while testing the code on a brand new Arduino UNO.