DIY Project 91

Adding a shock/motion sensor to the stock alarm

by southpawboston    (difficulty: medium)

There are different types of sensors that vary in how they detect intrusion. Shock/motion sensors typically work by triggering a shock-sensitive piezo switch that trips the alarm. Glass-breakage sensors use sound pressure detection to trip the alarm. Intrusion sensors are common with convertibles, and detect motion inside the passenger compartment, using either infrared or doppler radar. Either way, they act as switches that send a ground signal to trip the alarm. They all require constant 12V and ground, and also need to tap into an existing alarm “trigger” (e.g., hood switch). Since the Elantra factory alarm has no additional trigger inputs, you will have to splice the sensor into one of the existing triggers. I prefer using the hood switch, since it's a simple ground circuit.

To do this DIY, first view and print out the club's "Tapping into the "ETACS" DIY. The ETACS module is a central module that controls the Elantra's alarm, central locking, and lighting systems.

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Materials and tools needed:

·     shock/motion sensor
·     electrical tape
·     crimp tool
·     solder
·     soldering iron
·     nylon snap ties (recommended)

Recommended Sensors: A high-quality sensor from DEI, Omega or Crimestopper can be found for under $20. Some shock sensors are "dual-mode", meaning they have two independent triggers: one for "low" impact (e.g., parking lot bumps), the other for "high" impact (e.g., door slamming, getting towed). The Elantra factory alarm can only use a single-mode shock trigger, which gets spliced into the hood trigger. You can install a dual-mode sensor, but you can only hook up one of the two triggers. Prices vary depending on the type of sensor you want.

Total cost: less than $25

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Procedure:

1.   Following the club's "Tapping into the ETACS" DIY, remove the dash fascia, CD deck, and HVAC controls. Unplug wiring harnesses "A" and "C" from the ETACS.

2.   Refer to the ETACS Harness Pin Table for ETACS pin locations. Using your sensor wiring instructions, splice the sensor harness wires into some or all the following ETACS pins, depending on the requirements of your sensor. Most single-mode sensors have only three wires and will only require splicing into pins A1(12V const), A16(ground), and C7(trigger input). [NOTE: If the sensor includes an "alarm armed output" wire, splice that into A16as well. If the sensor includes a "12V ignition ON" wire, splice that into A5.]

3.   After all splice junctions are properly soldered and taped, mount the sensor. The sensor can be mounted anywhere. Since most sensors are adjustable for sensitivity, you will want to have quick access to it to be able to fine-tune its sensitivity after it's installed (somewhere under the dash near the steering column will allow easy access while keeping the unit nicely tucked away). It should be screw-mounted solidly to part of steering column support or dash frame, so it's sensitivity to impacts is maximized. Securing the sensor with snap-ties to a wiring harness or other "loose" surface will decrease its sensitivity to shock.

4.   Secure any loose wiring to existing wiring harnesses with nylon snap ties or electrical tape.

5.   Re-assemble the CD deck, HVAC controls, and dash fascia.

- southpaw