Upgrading a 2004 Subaru STI with a DIY Proximity Unlock System

Nick grabbed a couple of Arduino Nano 33 BLE boards and added his own DIY proximity unlock feature to his 20-year-old Subaru STI.

Cameron Coward
11 months agoAutomotive / Sensors

Nick has a really sweet Subaru STI (GDB), which is the kind of car that every JDM and rally racing enthusiast loves. But while that is fast for the era and handles like a dream, it is still 20 years old and seriously lacking in modern amenities. Among the many convenience features that have since become common is proximity unlock and Nick was tired of having to reach into his pocket every time he got in the car. At the risk of purist scorn, Nick added his own DIY proximity unlock feature.

Nick’s STI already had electric door locks — it isn’t that old. He just needed a way to remotely press the switch when he got close. There are many, many different ways in which Nick could have approached this, but he ultimately decided to use Bluetooth as a tool for proximity detection.

This system requires one Arduino development board and one portable device with a Bluetooth Low Energy (BLE) adapter. In this case, that first board is an Arduino Nano 33 BLE that goes inside the car. For the second device, which the driver must carry, Nick tried both a smartphone and another Arduino Nano 33 BLE. When the second device connects to the first via BLE, it is safe to infer that they’re fairly close to each other. When the RSSI (Received Signal Strength Indicator) gets high enough, it is safe to conclude that they’re so close that unlocking the doors is appropriate.

Security is definitely a concern here, as BLE lacks robust protection and BLE devices are easy to spoof. But we can’t imagine that a would-be thief would even think to try — they’d have no reason to suspect that this classic has a DIY proximity unlock system.

With that in mind, Nick connected the first Arduino to the car. It receives power from the car’s 12V battery through a buck converter that spits out 5V. It then “presses” the door unlock switch (on the driver’s side door panel) using a basic 12V relay module. As far as the car knows, this is exactly the same as the driver pushing the actual button on the door. For that reason, there isn’t any reason for the car’s primitive antitheft security system to raise an eyebrow.

The STI used to represent affordable hooning, but classics like this one are now pretty darn special. Though it will upset some, Nick’s STI is now one of a kind with a feature that every other GDB owner will secretly envy.

Cameron Coward
Writer for Hackster News. Proud husband and dog dad. Maker and serial hobbyist. Check out my YouTube channel: Serial Hobbyism
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