The eight digits 86211803 identify a Xiaomi Redmi Note 4. A phone whose IMEI starts with them is that model, whatever the seller wrote in the listing — the TAC is the manufacturer’s own allocation, not a lookup table someone typed by hand.
Have the full IMEI? The free TAC / IMEI lookup resolves it and returns the specification sheet. For the lock state, use the $0.03 SIM lock check — a model lookup cannot tell you whether the handset is carrier locked.
What a TAC cannot tell you
Three things decide whether a device is worth buying, and none of them is in the TAC: whether it is carrier locked, whether it is blacklisted, and whether iCloud or MDM is on. Those are separate records against the full IMEI, and each costs a few cents to read.
Carrier lock — the operator that owns the activation policy, from $0.03.
Blacklist — GSMA and carrier registers, from $0.03.
iCloud / MDM — the locks no unlock service can remove.
