YOUR SPEED. YOUR DEVICE.
Does a GPS Speedometer Work Without Internet?
Yes, GPS itself works without internet. Satellites broadcast one-way signals and your phone calculates its position from them, so no data connection is needed for the measurement. A browser speedometer also needs its page and scripts on the device, which means Xpeed opens offline only on pages you visited while online, and it still depends on the phone receiving a usable location.
XpeedGPS does not send anything back
GPS.gov describes GPS satellites as transmitting one-way signals that carry the satellite's position and the current time. The receiver in your phone uses that information to calculate its own three-dimensional position and time. Nothing is uploaded to the satellites, and the civilian service is free for everyone.
That is why a phone can find its position in a place with no mobile coverage. GPS.gov gives a typical accuracy of 4.9 meters (16 feet) under open sky for GPS-enabled smartphones and notes that accuracy gets worse near buildings, bridges and trees.
What changes when the phone has no data connection
Phones rarely rely on satellites alone. Apple says Location Services on iPhone can use cellular, Wi-Fi, GPS and Bluetooth information. Google says Android's Location Accuracy service uses Wi-Fi access points, cellular towers and GPS together with sensor data, and that it mainly helps indoors and near large buildings where GPS is weak. With that service turned off, Android uses only GPS and device sensors.
In practice, satellite reception carries more of the load when you are offline. Apple notes that GPS accuracy depends on the number of visible satellites and that locating all of them can take several minutes. Go outside with a clear view of the sky and give the phone time before you judge the reading.
A browser tool also needs its files
A web page needs its HTML, scripts and fonts from the server unless they are already stored on the device. Offline use depends on a service worker, which MDN describes as a script that sits between the page and the network and can answer requests from a cache when the network is not available. Service workers run only on HTTPS pages, and the browser location API has the same requirement.
Xpeed's service worker follows these rules:
- Each public page you open while online is saved on the device. The cache keeps the 35 most recently saved pages.
- Scripts, fonts and images that a page loads are saved with it, including the code for the GPS tool.
- When the network fails, a saved page opens from the device. A page that was never saved shows a short notice saying it is not available offline.
- The contact page and the history page are never saved by the offline cache.
The footer of each page tells you the cache state. Online, it shows how many visited pages are available on this device. Offline, it says that cached pages can open, that GPS still needs a valid device location and that internet testing needs a connection.
How to prepare before you lose signal
Set things up while you still have a connection:
- Open the speedometer page you plan to use, for example the car or boat mode, and wait for it to finish loading.
- Press Start once and allow location. The browser remembers a granted or denied permission, so it will not have to ask again offline.
- Check the footer line for the number of saved pages.
- To try it, turn off Wi-Fi and mobile data, reload the page and press Start outdoors.
- Keep the page visible during the trip. Browsers may pause location in a hidden tab or on a locked screen, and Xpeed stops its location watch while the page is hidden.
What does not work offline
The internet speed test needs a connection by design, since it measures data sent to and from an M-Lab server. A page you have never opened cannot load. Contact forms cannot be sent. Clearing the browser's site data removes the saved pages, and you will need to open them online again.
A saved page is also no proof of reception. In a tunnel, an underground station or a building with few windows, the phone may report no location at all. Xpeed shows a dash when there is no recent valid reading and keeps zero for a measured zero speed.
What this guide is based on
This guide describes the service worker code that Xpeed ships, the browser documentation from MDN and the GPS and phone documentation listed below. It is not a field report from a specific tunnel, flight or phone model. Offline behavior depends on the browser and its storage settings, so check your own device before you rely on it.
Questions and answers
Does a GPS speedometer use mobile data?
The satellite measurement itself uses no data. Loading a page for the first time, downloading map tiles or sending results does. Once an Xpeed page is saved on your device, reading speed from it needs no mobile data.
Will Xpeed work in airplane mode?
It depends on whether your device keeps GPS reception available in airplane mode and whether the page was saved beforehand. On a flight, follow the crew's instructions about devices first.
Why does the first reading take longer without internet?
Phones can combine GPS with Wi-Fi and cellular signals, which helps most indoors and near large buildings. Offline, the phone may have to rely on satellites alone, and Apple notes that finding all visible satellites can take several minutes. Open sky helps.
How many pages does Xpeed save for offline use?
Up to 35 public pages that you opened while online, per browser. The oldest saved page is removed when a new one is added beyond that limit.