Inter-operation between the heterogeneous wireless networks and systems available now and in the future is of considerable interest. Fundamental to such work is the ability to discover available alternative systems, and to monitor these modes to determine whether they are more attractive in some way than the current system. This paper presents a survey of different solutions to the problem of multi-mode detection and monitoring including blind unassisted techniques, co-operative devicefederation approaches and higher-layer mechanisms and suggests future research directions in this area.