GPS Tracker Indoor Accuracy: How WiFi Positioning Works
Share
Satellite GPS is unreliable indoors because walls, metal and concrete block and scatter the signal. Modern trackers work around this by switching to Wi-Fi positioning, which reads nearby wireless networks instead of satellites, and falling back to cell-tower triangulation where neither is available. Tack GPS locates to within 3 to 5 metres outdoors and 10 to 30 metres indoors using Wi-Fi positioning.
That switching happens automatically. You do not choose a mode, and in the app you simply see a location. What follows is what is happening underneath, and why the accuracy figure changes depending on where the tracker is.
Why does GPS fail indoors?
Outdoors, GPS is accurate because satellites broadcast signals with a clear path to the device, which calculates position from how long each signal takes to arrive. With open sky, accuracy within 5 to 10 metres is normal.
Indoors, that path is broken. Thick walls stop most satellite signals, and the ones that get through bounce off interior surfaces first, arriving late and from the wrong direction. The tracker is then working from contradictory data, and the position it reports can be a hundred metres or more from reality. In a multi-storey building, satellite GPS also cannot tell you which floor someone is on.
For elderly care that gap matters. A 150 metre radius in a shopping centre is not a location, it is a search area.
How does Wi-Fi positioning work?
Wi-Fi positioning does not use satellites at all. It uses the wireless networks already broadcasting inside buildings.
The tracker scans for nearby networks without connecting to any of them, records their identifiers and signal strengths, and compares that pattern against a global database of known network locations. Because every spot has a slightly different combination of visible networks and strengths, the pattern acts as a fingerprint. The more networks in range, the tighter the match.
This is statistical matching rather than triangulation in the GPS sense, and it has one useful property: Wi-Fi signals pass through walls, so it keeps working on every floor of a building where satellite signal does not.
What happens where there is no Wi-Fi?
Wi-Fi coverage is dense in cities and sparse in rural areas, forests and open countryside. In those places the tracker falls back to cell-tower triangulation, using its own cellular connection to estimate distance from nearby towers.
Cellular is the least precise of the three, typically giving an area of 100 to 250 metres rather than a point. It is not good enough to find someone in a building, but it is enough to tell you which part of which town to search, and it works almost anywhere with mobile coverage.
How hybrid positioning combines all three
Trackers like Tack GPS Plus run all three methods and use whichever is most reliable at that moment:
- Open sky: satellite GPS, 3 to 5 metres
- Indoors: Wi-Fi positioning, 10 to 30 metres
- Remote areas: cell-tower triangulation, roughly 100 to 250 metres
The switching is continuous and automatic. The practical result is that the dead zones which affect GPS-only trackers, car parks, malls, hospital interiors, mostly disappear. Tack GPS Plus also adds an Indoor Elevation Finder for identifying which floor someone is on, which none of the three positioning methods can do on their own.
What accuracy can you actually expect?
| Environment | Method in use | Typical accuracy |
|---|---|---|
| Open sky, park | GPS | 3 to 5 metres |
| Shopping mall | Wi-Fi | 10 to 30 metres |
| Dense office building | Wi-Fi and cellular | 20 to 50 metres |
| Remote countryside | Cellular, GPS where visible | 100 to 250 metres |
| Underground car park | Wi-Fi where available | Variable, often limited |
These are typical figures rather than guarantees. Accuracy in any specific building depends on how many wireless networks are in range, and underground spaces with no Wi-Fi remain genuinely difficult for any tracker.
Frequently asked questions
Does Wi-Fi positioning work if the tracker is not connected to Wi-Fi?
Yes. The tracker only needs to see the networks, not join them. It scans for nearby access points and uses their known locations to estimate position. Scanning is also faster and uses less power than connecting would.
How accurate is Wi-Fi positioning in a large building?
In buildings with many networks in range, such as offices, hospitals and malls, expect roughly 10 to 30 metres. In smaller buildings with few networks nearby, accuracy loosens considerably. Dense urban areas generally perform better than isolated ones for this reason.
What happens if there is no Wi-Fi coverage?
Cell-tower triangulation takes over. You get a wider area of roughly 100 to 250 metres rather than a precise point, but the tracker keeps reporting.
Does Wi-Fi positioning use less battery than GPS?
Yes. A Wi-Fi scan draws less power than holding a satellite fix, which is one of the reasons hybrid trackers can run for weeks rather than days while still updating location indoors and outdoors.
Does weather affect Wi-Fi positioning?
Not meaningfully. Wi-Fi signals travel short distances indoors and are largely unaffected by rain or snow, whereas heavy cloud and storms can degrade satellite reception.
Does Wi-Fi positioning work in other countries?
Yes. The network database is global, so positioning works anywhere with reasonable wireless coverage. What varies by country is cellular roaming, so check the roaming coverage of the specific device before travelling.
Choosing a tracker for indoor use
If the person or item you are tracking spends most of their time inside buildings, satellite specifications alone will not tell you what you need to know. Look for Wi-Fi positioning as standard, and for elevation detection if multi-storey buildings are part of the picture.
- Tack GPS Plus Global, hybrid positioning with Indoor Elevation Finder and fall detection
- Elderly care features, how families use safe zones and alerts day to day
- All features, geofencing, location sharing and tracking modes
