Porsche 993: Why Does My Alarm Keep Going Off?

This article applies to the Porsche 911 (993) (1993-1998).

If you’re reading this article, then chances are you’ve either had to or are otherwise presently dealing with the annoying headache of your Porsche 993’s alarm going off at random. There are many reasons why this might be happening, and how to go about resolving the issue. Before we get into some of the specific causes of a random alarm, note what the stock alarm monitors:

• Doors-Central Locking System
• Engine & luggage compartment lids
• Glove compartment
• Radio
• Ignition

As such, these areas should be checked for any sort of damage/peculiar conditions before considering some of the causes listed below. If the lights on the car do not flash when the car’s locked, or they double-flash after 10 seconds, it’s an indication that not all of these contacts have been closed. And if an alarm contact is interrupted, the horn will sound for four minutes while the interior and hazard warning lights flash a warning. It's worth noting that if the Porsche 993’s Central Locking system is not working, its alarm can be primed by performing three locking actions in rapid succession. The car’s lights will indicate priming complete by a double-flashing signal.

Per the Porsche 993 owner's manual, here are some of the more commonly cited reasons why an alarm randomly sounds in a Porsche 993, and how you might go about addressing the issue.

Interior Motion Sensors

There’s a chance your car might be picking up the motion on the inner cabin which, in turn, will set the alarm off. This could be something as simple as a bird flying above the car, a shadow cast on to a seat, or a flying insect caught inside. To fix this issue, try double-locking your car. This will automatically turn this part of the system off.

If your alarm no longer goes off, you’ve diagnosed the source of your problem.

If you don’t want to bring the car to the mechanic to have the system’s sensitivity re-calibrated, simply purchase a windshield sun deflector to keep the sun and all casting shadows out of the cabin. You may also want to leave the windows open for some time to ensure any and all flying insects make their way out of the car (in a secure location, of course).

Frayed Wires/Dying Battery

Porsche owners take good care of their prized vehicles and will often store them in places like their garage, as opposed to the driveway. While a good idea for the purpose of maintaining the physical appeal of the car, it does make it subject to critters and wildlife that might be living in the unit. As such, you should scan your vehicle for any loose or frayed wires.

Also, while looking at the wires, pay attention for frayed insulation, as this is often an indication of a possible short in the area. One area that commonly sees damage is the hood sensor. Any wear and tear will cause the alarm system to fire at random, particularly on rainy days when water might seep in and agitate the system.

And as long as you’re scanning the wires, take some time to check on the car’s battery status as well. A dying battery can fire off random power pulses which, in turn, set off the alarm system.

Pro Tip

A good thing to keep in mind when you’re checking all the wires is to label or otherwise keep a record of which wire goes where. This is helpful should you need to re-install the system in order to get it back to functioning normally again.

Dampness

Check for dampness under the seats and around the door bottoms. The alarm module is (typically) located under the passenger seat, and following a heavy rainstorm, the low spots in the already low-to-the-ground Porsche 993 are a risk for flooding/collecting water, especially if you’re getting in and out of the car during the storm itself, or if you have a loose door seal.

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