Location technology
Why GPS Does Not Work Well Indoors
Satellite signals are faint and walls absorb or scatter them. Learn why GPS struggles inside buildings and what phones use instead.
Updated 14 October 2026 · 3 min read
GPS works poorly indoors because satellite signals are already very weak when they reach the ground, and roofs, ceilings and walls weaken them further or scatter them. The receiver may hear too few satellites, or hear only distorted ones, and cannot calculate a position with confidence.
How weak the signal is
A GPS signal travels over 20,000 km from orbit and arrives at a strength far below that of a typical radio or television signal. Receivers can detect it in open sky because they are designed for exactly that. Reinforced concrete, metal roofing, coated glass and thick floors can reduce it enough that the signal drops below what an ordinary receiver can use.
Reflections inside and around buildings
Even when some signal gets through, it may arrive after bouncing around. This multipath effect distorts timing, in the same way described for urban canyons. The receiver may produce a position that is off by tens of metres, or it may place you on a different floor level than you expect, since height is the least accurate part of a GPS fix. See GPS altitude and elevation.
What phones do instead
Because satellites are unreliable inside, devices fall back on other sources:
- Wi-Fi networks: The names and signal strengths of nearby networks can be matched against a database of known locations.
- Cell towers: The towers your phone can see give a rough area, usually coarser than Wi-Fi.
- Bluetooth beacons: Some venues install small transmitters that apps use for room-level positioning.
- Motion sensors: Accelerometers and gyroscopes help estimate movement from the last known position.
The first two are described in how phones use Wi-Fi and cell towers.
Practical tips
- Move near a window or step outside before taking a reading you care about.
- Allow precise location and keep Wi-Fi switched on, even if you are not connected to a network.
- Wait a little for the estimate to settle.
- Remember that a reading taken inside a building may represent the building, not the entrance.
Why this matters for addresses
If you need to mark a delivery point, a reading taken from inside a building may be off, and an entrance may be on a different street from the room you are in. A better approach is to place a marker by hand on the entrance, zoomed in to the finest level. A location code then refers to the cell around that point. Learn more in how to find the coordinates of a place.
Frequently asked questions
Can GPS work inside a building at all?
Sometimes, near windows or on upper floors of light structures. Many phones can still produce a position indoors, but it is often less reliable and relies on other sources.
What do phones use indoors instead of GPS?
Typically nearby Wi-Fi networks, Bluetooth beacons, cell towers and motion sensors.