Cheap relay switch

[Mike65401]

What kind of relay switch will be able to close a circuit when the trigger will be the wire that normally goes to the alarm/buzzer in a smoke alarm? I want to have that trigger another lower pitched sound maker since I can't hear the high pitched alarm that's normally found in smoke alarms.

 

[Bluejets]

I can't hear the high pitched alarm that's normally found in smoke alarms.

There are smoke alarms available for hearing impaired with inbuilt bluetooth to drive pillow vibrators and flashing lights.

There are also ready made units which will interface with certain smoke alarms to drive egress systems for hostels and the like.

The interconnect (alarm) is associated with the mains wiring and should not be interfered with from the point of view of safety both from mains wiring and the proper working of the device.

Any device added to a smoke alarm circuit must match the existing alarms.
Just as any replacement smoke alarm must match the existing or complete system will require replacement.