Unknown Caller ID is an independent lookup service that helps people investigate unfamiliar US phone numbers. Its reverse phone lookup searches public records and databases for available information, which may include a caller’s name or aliases, city, state, ZIP code, carrier, and line type. Users enter a number to search, then can review the details available in a report. The service also offers an area code directory, allowing visitors to browse numbers by region and prefix, and a spam-check tool to help assess unknown calls.

Unknown Caller ID describes its searches as confidential, secure, and encrypted, and says people whose numbers are searched are not notified. It notes that results vary according to the number and the public records available; unlisted and prepaid numbers may have limited information. The company states that it is not affiliated with phone carriers and is not a consumer reporting agency. Its information is not intended for decisions about credit, insurance, employment, or tenancy. The site also participates in affiliate programs.