Why does car alarm go off when connect battery?

When a car battery is connected, the sudden influx of power can trigger the alarm system if it detects a change in electrical signals or if the system is designed to activate upon power restoration. Additionally, some alarm systems have a built-in feature that causes them to sound when they sense tampering or disconnection, which can happen during battery replacement. To prevent this, many alarms have a reset procedure that needs to be followed after reconnecting the battery.