A drone lands in a suburban backyard, drops a package, and takes off. Thirty seconds later, the delivery API logs a completion event with a GPS coordinate and a timestamp. The recipient files a dispute: package never arrived. Now what? GPS logs are trivially forgeable. Anyone with $25 of hardware off AliExpress can spoof a coordinate. The timestamp came from the same device that forged the coordinate. The only physical witness to the event is the drone itself, and the drone is back at the depot telling us everything is fine.
This is the core problem for every physical AI agent: drone delivery, warehouse AGV, autonomous mobile robot, humanoid assistant, inspection UAV. The moment you need to settle a payment or satisfy an audit, the agent's own claim about where it was is the weakest possible evidence you could produce. And that's before anyone is actively trying to cheat.
Proof-of-presence is the primitive that sits underneath physical-world settlement. It's what turns "I was there" into "here's the receipt, signed by physics."
Why GPS alone is a fiction
GPS was designed in the 1970s to guide cruise missiles. The civilian signal is unencrypted, broadcast at well-known frequencies, and can be overwritten by any transmitter that's close enough and loud enough. In 2011, an Iranian team landed a US RQ-170 drone by spoofing its GPS. In 2020, researchers demonstrated drive-by GPS spoofing on commercial navigation. In 2024, enough consumer-grade GPS spoofers were in circulation that commercial airlines started receiving cockpit warnings in areas with no military conflict.
The attacks aren't exotic. The defense isn't "better GPS" — the defense is not trusting GPS as the sole witness. You cross-check it against independent signals the attacker would have to compromise separately and simultaneously:
- Cellular tower triangulation (RSSI fingerprints of nearby eNBs).
- Wi-Fi beacon proximity (MAC + signal strength against a known map).
- Barometric altitude (hard to spoof from the ground).
- IMU dead-reckoning (integrates acceleration over time — any jump is visible).
- Visual odometry or LiDAR point-clouds against a ground-truth map.
If an attacker spoofs GPS but the cell-tower RSSI doesn't match, the proof fails. If cell towers are also spoofed but the barometer disagrees, the proof fails. Each independent channel you add multiplies the cost of a successful attack.
The six-layer receipt
GridStamp is organized around that same principle, borrowed directly from how mammalian brains actually encode location. The hippocampus doesn't rely on any single sensory channel for spatial memory — it builds a composite from place cells, grid cells, border cells, head-direction cells, and time cells, all of which can disagree, and disagreement is itself a signal. We turned that into six software layers:
SpatialProof
The raw multi-source fix: GPS + cellular + Wi-Fi + barometer + IMU collapsed into a single claim with a quantified confidence interval. No single channel is load-bearing.
PlaceCells
Semantic anchoring. The fix resolves to a known place — warehouse bay 4, delivery zone Z-7, customer GPS pin — not just coordinates. Prevents off-by-a-block delivery fraud.
GridCells
Trajectory continuity. Successive fixes have to be physically reachable given the agent's top speed and last known position. A drone that was in Austin two minutes ago can't produce a valid fix in Dallas.
AntiSpoofing
Active detection. Consistency checks across all channels, canary challenges (the agent is periodically asked to produce a fix against a secret reference beacon), and hardware-attestation where the signing key lives in a TPM or secure enclave.
MemoryConsolidation
Each verified fix becomes a node in a Merkle-chained memory log. Tampering with a single entry invalidates every proof that follows, so the entire history is as forgeable as the hash function underneath — which is to say, not.
Settlement
The signed, witnessed, chained receipt is the object a counter-party clears against. MnemoPay reads it, verifies it, and releases funds — or flags the gap and freezes the transaction for review.
Six independent layers, one Merkle-chained receipt. The physical world gets the same kind of proof a Stripe charge has had for a decade.
Where this actually matters
The near-term use cases aren't exotic. They're the places where somebody is already arguing with somebody else about whether a thing happened:
- BVLOS drone delivery. Beyond-visual-line-of-sight operations require FAA Part 135 or Part 108 authorization and every operator has to produce auditable delivery logs. "GPS said we were there" will not survive a subpoena. A signed six-layer receipt will.
- Insurance settlement. If an AGV damages inventory in a warehouse, whose insurance pays? The proof of which robot was where at 03:14 determines the answer. Today that proof is a time-synced camera feed and a lot of hoping. Tomorrow it's a receipt.
- Autonomous last-mile. Robotic sidewalk delivery has a chargeback problem: recipients claim the package never came, the robot says it did, there's no neutral third-party witness. A presence proof is the witness.
- Compliance for the EU AI Act. Article 26 requires logging of "the spatial and temporal conditions in which high-risk AI systems are used." A cryptographically signed proof stream is the compliant log. An unsigned JSON file is not.
This is the other half of the stack
If the agent credit score is the answer to "can I trust this agent with money?" — proof-of-presence is the answer to "can I trust this agent with the physical world?"
They're the same shape of problem. Both collapse an asymmetric situation — the counter-party knows far less than the agent does — into a falsifiable artifact the counter-party can verify without trusting anyone. Both work by producing receipts that the issuer can't forge. Both are primitives, not products. Products get built on top of them.
GridStamp is on npm today. Apache 2.0, six layers, TypeScript. Read the spec before you integrate it. If you're shipping a physical agent in 2026, you're going to need this — not because we say so, but because the first chargeback is going to convince you.
— Jerry Omiagbo