Can a car alarm drain the battery?

Yes. A car alarm can drain the battery over time because it requires power from the battery to power its electronics whether in standby mode or triggered.

The current draw in standby mode is much lower compared to when the alarm is triggered and sounding the siren or activating the hazard lights.

How long does it take a car alarm to drain the battery?

In standby mode, a car alarm can take several weeks to significantly drain a car’s battery. This is because they generally consume low currents (mA) and even then many have power save features that further reduce their power consumption.

When triggered, however, a car alarm can drain a car battery within a day or couple of days depending on:

  • what warning features are activated – siren, flashing lights or both
  • power consumption of installed siren (w)
  • the battery capacity
  • false alarm prevention features available in the the alarm model. Some car alarm models have inbuilt features to stop repeated triggering by suspected environmental conditions like thunder.

They reset and do not trigger if the same sensor is activated within a specified period. This reduces the drain on the battery.

For information on what else can drain a battery when it is off, find out here.

How to stop the car alarm from draining the battery

If you drive your car regularly, the current drain on the battery shouldn’t be of worry because of the relatively small amounts of current needed in standby mode.

You are at a higher risk of draining your car’s battery If:

  • your car is parked for an extended period without periodic recharging of the batteries (through regular driving)
  • your alarm is triggered from time to time by thunder or noises in the neighborhood

You can minimize the danger of draining your battery by:

  • reducing its sensitivity when the car is parked in a noisy environment
  • connecting your car battery to a battery maintainer to trickle charge and regular top up charge when your car is parked for a week or more.

Can a car alarm kill the battery?

A properly installed car alarm’s current drain is not likely to cause damage to a car battery from excessive discharging unless it is an aged or poor quality battery.

If your car is going to be left parked for a week or more, connect its battery to a battery maintainer to minimize the risk of damage to the battery.

Will the car alarm go off if the battery is dead?

If the car alarm has a backup battery then the alarm can still go off if the car battery is dead.

The backup battery continues to power the alarm’s electronics when the car battery fails or is disconnected.

Frequently asked questions

# 1. Why does my car alarm go off when I disconnect the battery?

Some car alarm systems have a sensing feature that detects changes in voltage in the car’s electrical system such as when the battery is disconnected.

This feature intends to deter attempts to disarm the alarm by disconnecting the car battery.

Check your car alarm manual to confirm if this is the case.

Fortunately, this is usually a programmable feature that can be turned off if you experience false alarms.


How to stop the car alarm from going off?

Depending on your car alarm model, it may be possible to stop your car alarm from going off by:

  • turning off the voltage drop feature ( if your car alarm has it)
  • disabling the alarm or turning off the battery backup siren (if your alarm model has it)

# 2. Why does my car alarm go off when I charge the battery?

This may happen when the car alarm is starting up as the battery is being charged after draining flat.

In this case, the siren will go off for a short time or can be switched off by disarming the alarm.

Otherwise, once the car alarm is connected to a stable (12V) supply, changes to the battery voltage as it is charged should not trigger the siren.

# 3. Do car alarms go off when the battery is low?

Some car alarms go off when the battery is low when the voltage drop feature is switched on. In this case, the voltage drop is interpreted by the alarm as an attempt to disable the alarm.

Check your car alarm’s manual to be sure.

If this is causing undue stress to you and the likelihood of tampering with the car’s battery system is low then you may disable this feature.

In general, a car alarm can drain the car’s battery over a long time especially if the alarm is in standby mode. You can reduce the risk of draining it flat by connecting the battery to a battery maintainer or trickle charger.

Related Questions

How long a car battery lasts with the ignition switched “ON”
What can drain a car battery
Estimating how long a battery lasts with different appliances

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