I have a number of BRK Smoke and Heat detectors which are interlinked to all sound on activation of any detector, I needed a way of linking the detectors to my house alarm which in turn would alert me on the mobile app.

A quick Google search flags a BRK RM4 relay interface which is triggered by the interconnect wire, the problem is they are only for the US market and work at 120v AC, this was confirmed with a phone call to the UK BRK representative.

I decided to take a punt and bought a RM4 from a US vendor, this took ages as a large number of seller just wouldn’t entertain shipping to the UK.

The moment the RM4 arrived, it was cut open 🙂

After checking the component data sheets the only parts which needed upgrading were the 2.2uF capacitor from 50v to 250v and the relay from 120v AC to 240v AC (part 369-337: G2R-2 230v).

Before swapping the parts I set up a ‘rough and ready’ test rig using a variostat to provide 110v AC to the RM4, a clamp meter was used to measure RM4 consumption and a 9v battery ready to place a voltage on the interconnect wire simulating an alarm condition, this worked fine.

After exchanging the capacitor and relay the RM4 was back on the rig and the supply voltage gradually increased to 240v AC while keeping a close eye on the current consumption which slightly increased from 2.8mA to 3.3mA.

The interface works as expected and the relay energises when a voltage is on the interconnect wire, it must be noted that the interface requires a supply voltage for it to work, the relay will not work in a power outage.

The RM4 wires are coloured for the US market and required sleeving with UK colours:

• RM4 Relay White wire = UK Blue Neutral
• RM4 Relay Black wire = UK Brown Live
• RM4 Relay Orange wire = UK BRK White Interconnect