This is from a system i seen with mixed addressable brands. Not legal but somehow the oem checker on the panel isnt active so it is not faulting.
System sensor (LST) 2251
Notifier SDX-751
Notifier NFXI-OPT which replaced an SDX-751
System Sensor (LST) 22051 which replaced an SDX-751
Notifier M500KAC call point
LST 200AP series call point which replaced a Notifier M500KAC
LST 200/500 german style call point which somehow came original to the building even though the building was originally notifier.
All of the detectors came from the same part of the building which was a starbucks. Weird system it was. Couldnt see the panel but the panel i belive is a notifier. The first 6 pictures was on the notifier and the 7th was on a LST panel on clip protocol which is also original to the building. there were also 2251s and 22051s on the LST while the notifier had all listed above. Somehow it passed inspection. The reason this might have happened is that the servicing company used notifier and switched to LST and needed to replace devices (which where the system sensor detectors came from) or that the building switched company from a notifier dealer to an LST user and needed to replace detectors and knew that it works.
If you have systems with mixed system sensor brands please post.