Go to checkcoverage.apple.com or use Apple Support app. Enter SN: [insert number] Verify: Model, warranty, purchase date, and any service lock/activation status.
Check the underside of the charging case or the device's surface. serial number check apple
Unlike carrier blacklists (which track stolen phones via IMEI), Apple’s public serial number check does not flag a device as "stolen" unless it is activation locked. Police and insurance companies have access to a separate, private database (GSX), but the average consumer does not. A device can pass a serial number check (valid warranty) but still be carrier-blacklisted for non-payment or theft. Go to checkcoverage