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Ver en españolRev 3.1 · ATtiny84A watchdog + Bluetooth LE
The GT-1 sits in series with your ignition line and listens for a Bluetooth heartbeat from your phone. Walk out of range and the engine is dead on the next start — no SIM card, no cloud account, no monthly fee.
How it works
There is nothing to press and nothing to remember. While your phone is connected the module keeps beating; the moment the pulses stop, the device arms itself.
Your phone talks to the module over Bluetooth Low Energy. No account, no cloud, no SIM — the link never leaves the car.
While the app is connected the module's STAT output pulses HIGH for about one second, roughly every five seconds. Every pulse counts as “still authorised”.
Ten seconds without a pulse and the state machine is ARMED. What happens next depends on the mode you ordered.
The next pulse returns the device to DISARMED — the relay releases and the normally-closed contact restores the ignition line.
Two behaviours
The operating mode is a firmware constant burned into the microcontroller — nothing on the board can be flipped after the fact, so pick one per unit when you order.
Calm mode
If the engine is already running when the link drops, it keeps running. The ignition line is cut only on the next start attempt while the device is still armed.
Best for Daily drivers, taxis, ride-hailing and delivery cars — anyone who cannot afford an engine that dies mid-route because a phone battery ran out.
Aggressive mode
The moment the phone leaves range a roughly 60-second timer starts. If the ignition is on when it expires, the relay cuts the ignition line.
Best for Vehicles parked overnight in high-risk areas, and owners who want the engine to die while the car is being driven away.
One mode per unit. Timing is derived from the microcontroller's internal watchdog RC oscillator, so the 10 s and 60 s windows are approximate — around ±10 % in practice, which is intentional for this revision. No crystal-accurate clock is used.
Fail-safe by design
Every layer of the GT-1 is built so that the failure direction is “the vehicle keeps working”, not “the vehicle is dead”.
With no power at all the contact 30 → 87a stays closed, so a dead module, a blown fuse or a removed battery leaves the ignition circuit exactly as the factory built it.
The only link is local Bluetooth Low Energy. There is no GSM radio to jam, no server to block, no data plan and no subscription that can expire or go unpaid.
A 2.7 V reset supervisor plus the brown-out fuse hold the microcontroller in reset while the pack is flat, so a sag, a recharge or a battery swap always ends in a clean boot.
A P6KE24A TVS for load dump, a series diode for reverse polarity, BAT85 clamps on the ignition sense and two snap-on ferrite beads on the way in.
DISALLOW is pulled low by a 100 kΩ resistor, so the relay cannot be energised while the MCU is in reset, being programmed, or un-programmed.
One honest limitation. An immobiliser cannot stop a tow truck or someone who finds and removes the module. What it does stop is the easy drive-away theft: without an authorised phone in range, the engine will not start — even if the module has been disconnected from the vehicle battery, because the watchdog runs from its own 1S Li-ion pack.
Real hardware
No development kit taped to a breadboard: the whole device — 12 V side, relay driver, microprocessor and Bluetooth module — is a single dual-sided board, and every pad is snapped to the hole grid of the panel photographed below.
Specifications
Taken straight from the engineering specification of revision 3.1 — no marketing round-up of the numbers.
| Microcontroller | Microchip ATtiny84A, 8-bit AVR — watchdog, timer and state machine |
|---|---|
| Radio | Bluetooth Low Energy module with a STAT heartbeat output |
| BLE supply | MCP1700 3.3 V LDO, 250 mA — 3.3 V at the module, peak draw under 50 mA |
| Logic supply | 1S Li-ion pack, 3.4–4.2 V, filtered by a snap-on ferrite |
| Reset supervision | MCP100 2.7 V open-drain supervisor + 10 kΩ pull-up |
| Ignition sensing | 390 kΩ / 68 kΩ divider with a 100 nF filter, compared against the 1.1 V internal bandgap |
| Programming | AVR ISP 6-pin header (MISO, SCK, MOSI, RESET, VCC, GND) |
| Status LED | Optional 3 mm indicator, on exactly while a cut is being requested (Pro build) |
| Relay | 12 V automotive SPDT, 30 A contact, terminals 30 / 85 / 86 / 87 / 87a |
|---|---|
| Contact mode | Normally closed — unpowered relay passes the ignition feed straight through |
| Relay driver | BC517 Darlington with a 10 kΩ base resistor and 68 kΩ bleed to ground |
| Coil protection | 1N4007 plus FR107 fast-recovery flyback diodes in parallel |
| Load dump | P6KE24A 24 V, 600 W TVS diode |
| Reverse polarity | 1N4007 in series with the 12 V input |
| Transient clamps | 2 × BAT85 Schottky on the ignition sense node |
| EMI | 2 × 5 mm snap-on ferrite beads (12 V input lead and logic rail) |
| Heartbeat pulse | ~1 s HIGH, repeating roughly every 5 s while authorised |
|---|---|
| Arming delay | ~10 s without a pulse |
| Power-on grace | ~10 s disarmed so the app can reconnect after a battery swap |
| Aggressive timer | ~60 s after the state becomes ARMED |
| Time base | Internal watchdog RC oscillator, ~250 ms tick — approximate by design |
| Board | 50 × 70 mm, dual-sided copper, front-mounted components |
|---|---|
| Relay mounting | Off-board, flying leads soldered to the board pads |
| Connections | 2-pin battery input, 6-pin BLE header, 6-pin ISP header |
| Vehicle system | 12 V negative ground (passenger cars, pickups, vans) |
| Consumption | BLE module under 50 mA peak; the logic runs from its own pack |
Installation
The GT-1 goes in the ignition feed — not in the starter, not in the alarm and not in the fuel pump. The original fuse stays in series.
Locate the wire that feeds the ignition circuit at the fuse box. Confirm it goes dead when the key is removed.
Splice the source side to relay terminal 30 and the load side to 87a. The original fuse stays in the circuit; the relay never carries the starter current.
Run the 12 V input lead through the supplied ferrite bead to the board, and the coil wires to terminals 85 and 86. Bolt the ground to the chassis.
Plug the 1S Li-ion pack into J1, pair your phone with the app, and check that the heartbeat keeps the relay released before closing the panel.
Professional installation recommended. The GT-1 must be installed on a vehicle you own or are authorised to modify. Cutting the wrong wire can damage the electrical system.
Check your local rules. Immobilisers are widely used and legal for your own vehicle across Latin America, but requirements and insurer conditions vary by country. Confirm the rules that apply to you and tell your insurer before installing.
Fitted by an installer? Everything you need — the colour wiring diagram, the relay terminal map and the ISP programming pinout — ships printed in Spanish with every unit, and the same diagrams are on this page.
Pre-order
The first test batch is being assembled now. Reserve a unit and we will confirm stock, shipping cost to your country and the right wire for your vehicle before you pay anything.
$89 USD
Status LED omitted — the lowest possible drain from the logic pack while a cut is active.
$109 USD
Status LED fitted: it lights up exactly while the device is asking for a cut, which installers love.
Prices are in US dollars for shipments inside Latin America and include the batch test report. Shipping is quoted per country after your reservation. Do you need several units for a fleet? Ask about the volume price.
Fill in the form and we will open WhatsApp with your reservation ready to send. No payment now, no card details, no account: we answer personally, in Spanish or English.
Latin America
Orders are packed by hand in small batches and shipped with door-to-door tracking. Support is in Latin American Spanish, on WhatsApp, with the person who built your unit.
Can't see your country? Ask — we ship to the rest of the region by quote.
Prices are quoted in US dollars, the way hardware is priced across the region. Import duties, if any, are set by your country's customs and are not included.
We are building a list of installers per city who have fitted the GT-1. Tell us where you are during your reservation and we will share the closest one.
Questions
Any vehicle with a 12 V negative-ground electrical system and a reachable ignition feed: cars, pickups, SUVs and vans. Tell us the year and model with your reservation and we confirm the exact wire before shipping. For 12 V motorcycles, ask us first — the relay and harness are sized for car currents.
No. The only link is Bluetooth Low Energy between your phone and the module inside the car. There is no data plan, no monthly fee, no app account and nothing to renew. The device keeps working in a garage with no signal, which is exactly where cars get stolen.
About 10 seconds without a heartbeat and the device is armed. In CALM mode an engine that is already running keeps running and is cut only on the next start attempt; in AGGRESSIVE mode the relay cuts the ignition 60 seconds after the link is lost. Get back in range with an authorised phone and the device disarms immediately.
The logic runs from its own 1S Li-ion pack, not from the car battery, so the watchdog keeps working even if someone disconnects the vehicle battery — that is the entire point. The vehicle only supplies the relay coil, and only while a cut is actually being requested.
Every immobiliser can be defeated by a tow truck, or by someone who finds and removes the module. The GT-1 makes a quick drive-away theft impossible and buys you time; treat it as one layer of security, not a substitute for parking carefully and insuring the vehicle.
Immobilisers are widely used and are legal for your own vehicle across most of Latin America, but the rules and the requirements your insurer imposes differ by country. Check the local regulations that apply to you and mention the installation to your insurer before fitting it.
Any 12 V auto-electrician can fit it in under an hour with the printed Spanish wiring guide that ships in the box; the whole job is one cut and one splice in the ignition feed. If you are not comfortable working on the vehicle's electrical system, have it installed professionally.
On the Pro build a 3 mm LED lights up exactly while the device is requesting a cut — in calm mode during the start attempt that gets blocked, and in aggressive mode after the 60-second timer expires. It is a diagnostic aid for whoever installs and tests the unit, and it draws only about 1–2 mA while active. The Basic build omits it to save pack energy.
This is a working revision 3.1 prototype heading into a 100-unit test batch. The production decision on the status LED and a tighter time base (an external 32.768 kHz oscillator for crystal-accurate timing) will be taken after that batch reports back. Reservations are taken in order and you will be told exactly which build you are getting.