Two smoke detectors located next to each other in a house.

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This house has two smoke detectors located next to each other, one on top, one on the bottom. Image 9 and image 16. Seems strange. Must be overkill if they both go off.

The bottom one is definitely a smoke, but is the top one the doorbell chime?

one ion, one photo maybe?

I think of one them might be just carbon monoxide and the other just smoke.

It appears someone didn’t bother taking the old one off the base when they replaced it.

The one on the top looks like an old (likely ionization) smoke alarm. The one on the bottom looks like a FireX smoke alarm, but you can’t tell if it’s ionization or photoelectric without looking at the back of that one. Either way, both of them are past their life expectancy.

I wonder if one was just disconnected.

In my area, it’s common to see sets of two adjacent smoke alarms in houses that are equipped with security systems. In these setups, one of the smoke alarms is typically a standard 120V unit, while the other is a low-voltage unit connected to the security system (the System Sensor 2012JA is quite popular for these applications).

In this case, however, it’s likely that someone installed a new smoke alarm and simply forgot to remove the old one.

Yeah. It seems like someone when replacing the smoke detector instead of removing the smoke detector and installing a new one, they just installed a new one under the old one and left the old one up.

The old one is likely a hardwired smoke detector. Plenty of people have difficultly working with hardwired smoke detectors. Because of this, someone just installed a battery operated smoke detector under the old hardwired one.

Top is a FireX FX1218 or FX1020/FXW-1, bottom is a current gen First Alert. If the FireX is a FX1020 they might have installed the FA to get battery capabilities rather than just replacing the FireX.

For plenty of people, installing a battery-only operated smoke detector is easier than installing a hardwired smoke detector. Many people have difficulty working with hardwired smoke detectors. Because of this, they likely installed a battery-only smoke detector instead of replacing the hardwired one.

Yeah, my assumption is that one of them was replacing the other and they got lazy (see that in annual inspections). But also, could be because they wanted 2 alarms, one AC powered, and a battery backup one in case the power went out. I see that a lot also when I’m doing annual inspections.