Does where you carry your phone affect GPS accuracy?

The short answer

Yes, a little, and less than most people assume. GPS depends on a reasonably clear path between the sky and the phone's antenna, and anything with mass sitting directly over that antenna — your body, a dense pack, water, metal — attenuates the signal to some degree before it arrives. The effect is real. It is also, for almost everyone in almost every pack, a much smaller factor than tree cover, canyon walls or bad weather, which is why it rarely gets talked about with the same urgency.

The practical version: carrying a phone in a hand or a chest pocket generally gives it close to the cleanest view of the sky it can get short of holding it flat on your palm and looking straight up. Carrying it low and buried in a stuffed pack gives it the worst view most hikers will produce. Both still work. The difference shows up as a slightly noisier line and a few more of the small positional wobbles every GPS track already has, not as a track that stops recording or becomes unusable.

What is actually doing the blocking

Your own body

A human body is mostly water, and water absorbs radio signals at GPS frequencies more than air does. Carrying a phone in a pocket against your hip, with your body between the antenna and roughly half the sky, is a real if modest source of attenuation — the same reason a phone call sometimes sounds clearer when you turn the handset or move it away from your head.

What is stacked around it in a pack

A backpack itself is mostly fabric, which is close to transparent at these frequencies and barely worth worrying about. What is inside the pack is a different question. A tightly packed load — especially anything holding a lot of water, like a hydration bladder or bottles sitting right against the phone — adds another layer of the same absorption a body already causes. A phone sandwiched between a full bladder and your back is looking at the sky through two water barriers instead of none.

Metal is the one to actually think about

Metal is a far more effective blocker than fabric or a body ever is — a foil-lined pouch, an aluminium pack frame pressed close, or a case built around a large metal battery pack can shield a phone from a GPS signal almost completely rather than just weakening it a little. This is a different order of effect from everything else here, and the only one worth actively avoiding if you care about the recording.

How much this actually shows up on a recorded track

Weigh it against what tree cover does, since that is the bigger and better-known version of the same idea: a forest canopy sits directly overhead for the entire time you are under it, scattering signal off leaves and branches for the whole walk. A phone in a pocket experiences a similar kind of partial blocking, but from one side rather than from above, and a human body is a smaller obstruction than a canopy of trees. On open terrain, a phone in a pocket next to a phone held in a hand will usually produce two tracks that both sit convincingly on the trail, with the pocketed one carrying a touch more of the fine jitter every GPS track already has.

It starts to matter more when it stacks with something that is already degrading the fix — genuinely thick tree cover, a narrow canyon, or the first minute of a walk before the receiver has settled. Body or pack attenuation on top of one of those conditions is a worse combination than either alone, the same way bad weather and dense forest together do more damage than either by itself.

What actually helps

• Keep the phone somewhere with a reasonably open view of the sky if you care about a clean track — a vest pocket, a top pack pocket, or your hand. None of this needs to be strict; it is a small effect, not a switch between working and not working.
• Avoid a metal-lined pouch or a case built around a large metal battery pack for a phone you are actively using to record. That is the one item here large enough to be worth deliberately working around.
• Get the initial fix somewhere open before you stash the phone, the same advice that helps under tree cover. A receiver that already has a good estimate copes better with a partially blocked view than one starting cold.
• Do not reorganise a pack around this. A phone doing its normal job from inside a normal pack, next to a normal amount of gear, still produces a usable, trail-shaped track. This is a modest factor worth knowing about, not a reason to hold a phone in your hand for six hours.

None of this changes what a recording app can do about it — the receiver reports whatever the antenna can see, and no software correction turns a mostly blocked signal into a clean one. TrailCam records in the background for the whole walk regardless of where the phone sits, so this is really a question about where you choose to carry it, not about the app watching it. It is free to download.