So - when installing these things, where's the best place to put them on the ceiling? Googling suggests the closer to the middle, the better - but do people really have them in the middle of the ceiling in their living rooms? 
They're not exactly decorative (but then, nor is my artex ceiling, I suppose).
How often do you actually look at the ceiling, thobut?
Exhibit A: Detector on beacon/sounder base. It's quite noticeable when it's flashing, but pretty unremarkable the rest of the time, other than to tradespeople with an interest in smoke alarms. A typical audio-only consumer smoke detector is a lot less sticky-outy.
Exhibit B: Ceiling Cat. Went unnoticed by Postman Piers (who has the finely-tuned peripheral vision of a native sign language user) for the best part of a day, and by assorted CrinklyCubs for almost a whole hour.
Obviously since it's your house, anything new will stick out like a sore thumb for a day or two before blending into the background.
