Fire alarm by Clarendon Homes

Hi all
Clarendon built my home in 2015.
We have two fire alarms in a single level home.
They started chirping today !
I opened the cover and got the shock of my life (use with pun) when I discovered that the alarm was not hard wired. All it had was the usual 9 V battery.

For the last four years I had been thinking that both the alarms are hardwired. Even the cover of the alarm has the words “A.C. power”written on it.

Can anyone confirm if Clarendon hardwire their alarms ....

should this thing be in the contract, if yes, where should I look ?

Thanks you

Are you sure they aren't hardwired with a battery backup?

They typically chirp to let you know to replace the battery even if they are hard wired.

They should have a back up battery. So that if you lose power they still function.

Here’s a pic of one of them. No wires that I can see ...

The three little metal prongs just above the battery push up into the base when you close it. All the wiring is behind.
As others have mentioned the chirping noise is to alert you that the batteries have lost power and need replacing.