How Auto Alarms Can Cause a Dead Battery

by Tom Lutzenberger
itstillruns article image
dead battery image by Katrina Miller from

Nothing is more frustrating and confusing than when you approach your car after it has been parked overnight, you click on your alarm key fob to disarm it and you hear an odd or slow warble instead of the traditional beep-beep from your car. Then you try to start your car and the battery is just about or completely dead. This problem is very common, but there's no real fix for it. You just have to be prepared that at some point the dead battery syndrome may occur.


Many auto alarms have to stay in an "on" mode whenever the car is stationary and turned off. This on mode is automatically triggered when the car is locked. To power the alarm system, the wiring is hooked up to a lead from the car battery. This means the system is drawing battery power while the car is off and not charging the battery. Over time, this sapping of energy can lead to battery failure.


The most common occurrences of a dead battery from an alarm usually happen late in the life of the car battery. When a car battery gets to five or six years in age, it doesn't hold its charge as well. If the battery is already going bad, a car alarm drawing power while the car is off is going to put the old battery over the edge and make it nonfunctional for starting. Good car batteries won't show this problem, being able to handle the alarm system draw for much longer than being parked overnight or for a few days.

Installation Method

Many auto alarms are installed at the car factory, so the design of the alarm is integrated into the most power efficient hookup for that particular car. However, if the alarm system is installed as an aftermarket add-on, sometimes the mechanics can install the hookups in the wrong locations. This can cause the alarm system to draw more power from the battery than it needs. This mistake in turn can draw down car batteries much faster than normal.

Short-Circuit Problems

The not-so-common problem that can cause a battery sap with a car alarm is a short circuit. This is when a frayed wire causes an intermittent connection with another metal part. The charge to the system gets pulled out of the circuit and grounded into the car part or frame. If the connection lasts long enough, it can draw the battery until it is dead. Only a mechanic will find this problem by going through the entire wiring of the alarm, looking for the break or exposure. Replacing the car battery just continues the problem until the new battery dies as well.

Choosing Alarms

The best auto alarms for power efficiency and arguably security are those that cut the ignition of a car rather than just make noise when the car is bothered. With an ignition cut, the car goes nowhere unless it is towed. This involves much less power draw than a full-sensory model designed to make noise when the car is bothered. Consumers should weigh the features that come standard with a factory-installed alarm versus what is offered after-market. If you can find a car with a factory-installed alarm model and an ignition cut feature, that may be the best of both worlds, particularly for your car battery.

More Articles

article divider