Any immobiliser / security not programmed to ECU properly is just an added wire loom and when removed car return to normal mode of operation hence become worthless.
Secondary battery is used in many cars security systems i guess, i had a SAAB 95 in the past, it started to have a problem kicking the alarm late at night in freezing weather and problem located to hidden secondary alarm battery wasnt charged enough and system activated sensing tempering. replacement sorted the issue!