I designed a similar system a few years back to provide proof-of-presence. Imagine a block chain of devices at locations (an alibi lets say). All devices are miners and only devices in your vicinity (think BLE) can "confirm" "transactions" (your presence) on the chain.

As with anything public + blockchain it had all the Cryptoeconomics incentives problems you would expect and I never solved them.

Finding a lost device has much lower stakes than proving an alibi in court so I see how this model would work.