Bluetooth OBD-II adapter + app · Android first, iOS following
Every drive recorded on its own. Fuel cost per trip. A dyno from one pull. Fault codes in plain words. And an AI that reads the whole history and tells you what changed.
Nothing to buy yet. The waitlist is how you hear when there is.
0 samples0 rpm peak0 km/h peak
What we found
During testing on a 2016 Mazda 3, the engine computer had been adding roughly 12% extra fuel on every drive to make up for a lean condition.
No dashboard light. No fault code. A normal scanner would have reported nothing wrong, because by its rules nothing was.
Revnote reads long-term fuel trim on every trip and notices when it drifts. That is the whole idea. The car already logs everything. Something has to read it.
+12%LTFT
Trim has stayed high on every recent drive. The ECU is compensating for a lean mixture, which usually points to a vacuum leak, an ageing oxygen sensor or a dirty airflow sensor. No code has set. Worth a look before one does.
What it does
It plugs into the port under the dash and stays there. The app does the rest.
Each trip opens when the engine starts and closes when it stops: distance, duration, route, fuel used. Nothing to press, nothing to remember.
reads engine speed · vehicle speed · fuel level · phone GPS
Worked out from what the engine actually burned, not guessed from fill-ups. Put in your local price and every trip gets a number.
reads mass airflow · fuel trims · commanded air-fuel ratio
0–100 km/h, 0–60 mph, quarter mile. Every result comes with the uncertainty the sensors actually support, so you know when a tenth is real and when it is noise.
reads vehicle speed · engine speed · phone GPS
When a code sets, you get the system it belongs to, what usually causes it, and whether it is a pull-over-now or a look-at-it-this-month.
reads stored codes · pending codes · freeze frame
Fuel trims, coolant warm-up time, idle stability, battery voltage at start. Slow drift shows up long before a warning light would.
reads everything above, every trip
Ask why economy dropped last month, or what that noise might be. It answers from your car's own logs, not a forum thread about someone else's.
reads your trips, codes and trends
Dyno
Third gear, full throttle, lift before redline. Revnote takes engine speed and road speed from the port, the car's weight and gearing, corrects for drivetrain loss and drag, and returns wheel horsepower and torque across the rev range.
No rollers, no appointment. Run it again after an intake or a tune and see whether anything really changed. It draws an uncertainty band around the curve, because a road is not a lab.
$99–129CAD
One purchase for the adapter and the app. No subscription. Android first, iOS following.
Questions
If your car has an OBD-II port, it is a candidate. That means petrol cars sold in North America from 1996, most diesels from around 2004, and cars sold in Europe from 2001 for petrol and 2004 for diesel. The port is under the dash, usually on the driver's side.
The standard readings are the same across almost every make: engine speed, road speed, coolant temperature, fuel trims, fault codes. What varies is the manufacturer-specific data layered on top, which is where a lot of the interesting detail lives. That is exactly why the waitlist asks what you drive. It decides which cars we put on the bench next.
No. One purchase covers the adapter and the app, somewhere between $99 and $129 CAD. No monthly fee, no features held back behind a tier, no charge for a second car. Nothing is on sale yet, so the waitlist is the only thing to join today.
Revnote is built and tested as one piece: our adapter and our app together. Cheap ELM327 clones vary enormously in which parameters they expose and how quickly they can be polled, and the dyno estimate and fuel-trim tracking both depend on a high, steady sample rate. We would rather say that plainly now than promise broad third-party support and disappoint you later.
Fuel trim is the engine computer correcting its own fuel maths. It watches the oxygen sensor and adjusts how much fuel it injects. Short-term trim is the moment-to-moment correction. Long-term trim is the learned offset the car carries around with it.
A positive number means the engine is adding fuel because the mixture is running lean. A negative number means it is pulling fuel back because the mixture is rich. Within a few percent of zero is normal. Consistently past about 10% means something is off: a vacuum leak, a tired oxygen sensor, a dirty airflow sensor, a weak injector. That can go on for months without setting a code or lighting the dashboard. Most scan tools will show you the number if you go looking for it. Revnote reads it on every drive and tells you when it moves.
It is an estimate, not a measurement, and the app does not pretend otherwise. During a full-throttle pull it samples engine speed and road speed several times a second, derives how hard the car is actually accelerating, and combines that with the vehicle's mass, gearing, drivetrain loss and an aerodynamic drag model to get power at the wheels.
A chassis dyno measures torque against a known roller in a controlled room. A phone and an adapter infer it from a road with wind, gradient and traffic on it. So Revnote shows an uncertainty band rather than one confident number. Its real use is comparison: same road, same gear, same conditions, before and after a change. It answers whether something actually did anything far better than it answers what your car makes.
The OBD-II port stays powered on most cars even with the ignition off, so any adapter left plugged in draws a small standby current. On a healthy battery in a car that gets driven regularly, that is not something to worry about. If a car is going to sit for weeks, unplug the adapter. That advice applies to every OBD dongle sold, not just ours.
If your battery is already on its way out, Revnote will notice: it logs cranking voltage at every start, so a battery getting weaker shows up as a trend rather than as a morning you cannot leave.
Android first, iOS after it. There is no build on the App Store today and we are not going to invent a date we cannot keep. If you are on an iPhone, the waitlist is still the right place to be. We will write when there is something you can actually install.
Waitlist
Leave an email and we will write once, when there is something to buy.
The car question is real research, not a marketing field. Every manufacturer exposes different data over OBD-II, and some keep the useful parts behind their own protocols. Knowing which cars are waiting tells us what to put on the bench next.