Alarms and trackers: fitting one without creating new problems

A security system is the one piece of aftermarket equipment designed to run around the clock and to splice into circuits that control engine starting. So the cost of a bad installation here is higher than for any other device.

The main problem: drain

Alarms and trackers are permanently powered. That is normal — but only if their armed-state consumption is within reason.

Normal quiescent current for the whole car once the modules sleep is roughly 20 to 50 mA. A badly fitted alarm easily doubles that; covered in the parasitic drain article.

Signs of trouble:

• The car will not start after three days parked.
• The battery dies in a year instead of four.
• Modules never sleep — visible in diagnostics.

What to do: after installation, always measure quiescent current 30 to 40 minutes after the doors close.

A tracker with its own battery is a separate option: independent of the vehicle supply but needing maintenance.

Splicing into circuits

Every splice is a failure point. A twisted joint corrodes, gives an intermittent contact, and in time produces codes in systems nobody touched; mechanics in the aftermarket equipment article.

The rules:

• Soldered or crimped joints, not twists.
• Heatshrink insulation, not tape that unwinds with heat.
• Its own fuse for each power circuit.
• Earth to a factory body point, cleaned back.

What not to do: splice into airbag, ABS, or engine management circuits. Not superstition — those are circuits where switching transients have consequences.

The data bus

On modern cars, security systems often connect to the data bus instead of analogue splices.

The upside: fewer splices, fewer failure points.

The downside worth knowing: a badly configured or cheap module floods the bus with requests. The result is modules that never sleep, communication errors, and a flat battery.

In practice: after fitting such a system a scan is mandatory — it shows whether the network gained “noise”.

Immobilisers and bypasses

Remote start requires bypassing the factory immobiliser, and there is an important security nuance: a bypass module with a key embedded in the car reduces its theft protection.

Modern solutions work differently and need no key in the car — worth clarifying before installation.

How immobilisers work is covered in their own article.

What to check after installation

1. Quiescent current after 30 to 40 minutes.
2. Codes across every system — before and after; the main check.
3. Whether the modules sleep — by current and by behaviour.
4. Factory functions: central locking, windows, interior lighting.
5. After a week parked — does it start normally.
6. Where the module is mounted — not where water runs, and not where it is found in a minute.

In short

• Normal quiescent current is 20–50 mA; a bad installation doubles it.
• A twisted joint instead of a connector gives intermittent contact and stray codes.
• Never splice into airbag, ABS, or engine management circuits.
• A cheap data bus module stops the car’s modules sleeping.
• After installation, read codes across every system rather than just testing the fob.

Download the app — codes across every module and voltage are read with an ELM327 adapter over Bluetooth SPP on Android, before and after installation.