Double-loop fire detection systems can either be the capacitance/resistance type, or the gas filled detector type. They are inherently more reliable than single indication fire detection systems, as the loops run together, and if both of them indicate a fire, the indication is much more likely to be correct.

Depending on the MEL (Minimum Equipment List) of the aircraft/operator, flights can be undertaken with one loop broken, as the system can change logic from requiring both indications to just one. This does obviously reduce the reliability of the system though, so the crew must be careful in doing this.