That was why I’d chosen it.

I stepped down off the step stool and tucked the yellowed plastic into my coat pocket so I’d remember to toss it on my way out.

The new unit came with an instruction card about the size of a business card and a lens no bigger than the tip of a pencil.

I read the card two times.

Then I held my phone up under the ceiling until the app picked up the signal and asked me for a name.

“There,” I told the ceiling.