A system and apparatus for detecting the approach of a vehicle includes an encoded signal which identifies a vehicle or route, and which is used to distinguish from different vehicles and routes. A receiver detects transmission signals above a threshold level, and responsive to reception thereof checks for one or a plurality of codes that identify particular vehicles of interest. When a desired signal is received, an alarm or indicator is generated that alerts a person. When the indicator is terminated, a lock-out period prevents undesired re-activation of the alarm or indicator based upon the same code. Unique headers enable transmission and exchange of additional data, and logical text may be provided which enables more ready viewing of coded information. The present invention has industrial applicability to public and private transportation systems, whether for passengers or other cargo.