A cold start is a GPS receiver powering on with no usable satellite data, forcing it to download orbit information slowly from the satellites themselves.
A GPS receiver cannot calculate a position until it knows where the satellites are. That information — the ephemeris — is broadcast by the satellites at 50 bits per second, which is roughly the speed of a 1960s teletype.
Downloading it takes 30 to 60 seconds per satellite under perfect conditions, and you need at least four. Any interruption to the signal restarts the download for that satellite.
That is a cold start, and it is why a tracker can sit apparently doing nothing for several minutes after powering on.
| Type | What the receiver retains | Time to first fix |
|---|---|---|
| Hot | Valid ephemeris, recent position, accurate time | 1–5 s |
| Warm | Almanac and rough position, stale ephemeris | 20–40 s |
| Cold | Nothing usable | 1–5 min, sometimes never |
Ephemeris data expires after roughly four hours. A device powered off overnight wakes into a cold start regardless of how good its last fix was.
This is the part that turns a slow start into a broken tracker.
The download needs an uninterrupted signal for the full 30–60 seconds per satellite. Under tree cover, in a moving vehicle, or anywhere with marginal reception, the signal drops often enough that the download never completes. The receiver keeps restarting and never reaches a fix.
The symptom is a tracker that works fine in an open field and never gets a position where it is actually installed.
A-GPS downloads the same ephemeris over the mobile network in a fraction of a second, turning every start into the equivalent of a hot start. It also lets the receiver work at much weaker signal strengths, because it only has to measure signals rather than decode data from them.
This is why phones fix almost instantly and a cheap tracker sometimes does not. The hardware difference is real but secondary; the network assistance is the main effect.
It depends on a working data connection, which is where setups usually fail. A tracker with a misconfigured APN has no data path, cannot fetch assistance, and falls back to unassisted cold starts — while appearing completely healthy, because SMS still works. If a tracker is slow to report and inaccurate when it does, check the APN before suspecting the GPS.
Two consequences worth planning around.
The first position after a gap may be late. A vehicle leaving a garage in the morning might not report for several minutes. If a zone boundary is crossed during that window, the alert arrives late or the crossing is missed entirely, because the device never reported a position inside the zone to transition from.
Early positions are less accurate. A receiver that has just achieved a fix typically has poor HDOP and a wide accuracy radius, tightening over the following minute or two. The first position after a cold start is the one most likely to sit falsely outside a zone.
Both argue for the same thing: draw zones with generous margin, so a slightly wrong early position does not read as a departure. See GPS accuracy.
Last reviewed 7 August 2026.
A-GPS (Assisted GPS) speeds up position fixes by downloading satellite orbit data over the mobile network instead of waiting to receive it from the satellites themselves.
GPS accuracy is how close a reported position is to the true location, usually expressed as a radius within which the real position probably falls.
HDOP measures how favourably satellites are arranged in the sky, acting as a multiplier on positioning error — the same measurements give a far worse fix when satellites are clustered.
An APN (Access Point Name) is the setting that tells a SIM-equipped device which gateway to use for mobile data — and the most common reason a GPS tracker never reports.
Draw a zone, assign a phone or GPS tracker, and get a blip the moment it crosses the line. Free for 7 days.