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About this tool
Show your speed from GPS readings and keep a private trip log.
The GPS Speedometer reads your device's own satellite fix through the browser Geolocation API and logs a timestamped row of speed, latitude, longitude and position accuracy for every update your phone reports. Speed comes straight from the GPS receiver's Doppler-derived value in metres per second and is converted to km/h by multiplying by 3.6 — it is not estimated from distance between points. It is for anyone who wants a speed readout and a private trip trace without installing a tracking app that uploads the route.
Open GPS Speedometer on AltFTool — it loads instantly in your browser.
Open the page over HTTPS on a device with a GPS receiver and press "Start with permission", then allow the browser's location prompt.
Move outdoors so the receiver reports a velocity; every fix appends a row under "Live local readings" with high accuracy on and cached positions disabled.
Read each row's timestamp, latitude, longitude, speed in km/h and accuracy in metres — "Unavailable" means the device sent no velocity — then press "Stop sensor".
Each row carries the fix's accuracy radius in metres, so you can judge how much to trust the speed instead of reading a bare number.
When the device does not supply a velocity value the row reads 'Unavailable' rather than back-calculating a fake speed from two coordinates.
Coordinates are held in the page's memory only and are discarded when you stop or close the tab — there is no account, upload or stored history.
GPS speed is usually the more truthful of the two. Car speedometers are legally required to never under-read and typically show a few percent high, while a satellite fix reports actual ground speed. GPS accuracy degrades under bridges, in tunnels and beside tall buildings, which is why the accuracy radius in metres is logged next to every reading.
Because your device reported a position without a velocity value. The Geolocation API's speed field is optional — many laptops and desktops positioning by Wi-Fi or IP never populate it, and phones may leave it null until the GPS chip has a stable fix. Moving outdoors for a minute usually makes it appear.
Only in the current browser tab. Readings are kept in a rolling in-page buffer of the most recent 200 rows, with the newest 100 shown in the table, and nothing is written to a server or to permanent storage. Closing or reloading the page erases the trace.
The browser requires an explicit grant before any page can watch your position, and this tool requests a live watch with high accuracy enabled and cached positions disabled so every row is a fresh fix. It also needs a secure HTTPS context; geolocation is blocked on plain HTTP pages.