New Smoke Detectors

 When the old smoke detectors consistently went off with ordinary cooking, then chirped incessantly, it was time to make a decision.  Dismantle them and take my chances or get new ones.  In the decades since last replacement, technology has changed.  Home Depot had a selection, No Frills not among them.  Apparently new installations all allow AC power with battery back-up, though we have no wiring to connect this.  In some units you can change the battery without disassembling the unit.  My second choice.  Ultimately I opted for two basic detectors run with transistor radio batteries that came with each unit.  

The base that attaches to the ceiling seems pretty standardized.  I had screws remaining but on the lower level the screws were insecure so I just repositioned them using the base as a template. Other than not having a Philips head screwdriver worth using it installed.  Then activating the battery took some doing as the terminals were not labelled positive or negative.  It turns out the manufacturer inserted plastic guides so they would only fit one way.  Screw the business end to the installed base, test it with the little button, and we're safe until the contents of the stove sets it off.

I though the upper unit would be easier as the screws were already in their proper position.  All I needed to do was loosen them, take off the old base, put on the new base, and add the electronics.  I did not anticipate the old base adhering to the ceiling as a consequence of fresh painting we needed done last year.  Prying it off took some ingenuity and some work.  Once off the screws did not fit perfectly into the new base but close enough to keep it secure.  Perfectionists don't do well.  Made sure it wouldn't wiggle, then installed the battery and completed the assembly.  A quick test of efficacy and we now have a safer home.