Here in bonnie Scotland, Aico 10 year li battery smokes and heats, radio interlinked...there is no simpler system.
No redecoration, no raggling (chasing)of walls and ceilings, plastering, painting...
Just stick 'em up, pair them, walk away...I have never had a call-back on Aico yet.
OK, it's a very fast installation, so not a lot of money to be made, but the clients love them once you have sold the concept...especially the quick in and out and no other trades to make good. An extra ÂŁ200, against about 3 times that for making good for hard wired...and it leads to extra work from satisfied clients.