Abstract: A method of tracking entry to and exit from a confined space includes a portable radio beacon placed proximate to but outside the confined space transmitting a first radio signal with an identifier that is associated with the confined space. A mobile device receives the first radio signal, measures a first real-time value of a first measure of received signal strength or quality, and transmits a second radio signal with the identifier and the first real-time value. A base station receives the second radio signal, measures a second real-time value of a second measure of received signal strength or quality, and transmits data including the identifier, and the first and second real-time values. A computer receives the data, determines proximity of the mobile device to the confined space from the identifier, and determines whether the mobile device is outside or inside the confined space from the real-time values.