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Replacing BRK 600 and 700 Series Smoke Alarms


All smoke alarms, whether mains powered or battery powered, have a finite lifespan. They can only continue to function at optimum levels for so long. If your smoke alarms are older than 10 years you must replace them as soon as you can to remain protected. The focus of this article are the 600 series and 700 series mains powered smoke detectors from BRK. Given that they draw their power from the mains, the task of changing them can seem a bit daunting for the majority of us that aren't qualified electricians! Luckily, BRK alarms are carefully designed to make exchanging the alarm heads for fresh smoke detectors simple for those that wish to do so.

While mains powered smoke alarms installed from scratch (base plate and alarm head together) should only ever be installed by electricians, it is perfectly safe to exchange the smoke alarm head of the above BRK alarms yourself as long as you follow the manufacturer's instructions and switch off the fuse before doing so.

A quick note on safe practice when changing detectors heads

A continuous green light on the unit indicates your alarm is receiving mains power. This light allows you to easily tell when the mains power has been isolated. Always make sure to check the green LED is on prior to switching the fuse off. Checking the status of the green light before and after turning off the power allows you to confirm that the power supply has been successfully cut from the alarm base before you attempt to remove the alarm head.

CAUTION! If your alarms are interlinked, or interconnected, via a wire (i.e. not using the DS700RF wireless base) such that testing one alarm causes all alarms to sound, then care must be taken to ensure all mains power circuits which supply the alarms are turned off at the fuse. While it is recommended to install mains powered alarms onto a single, dedicated power circuit this is often not possible where the alarms are fitted in an existing property which did not previously have mains powered alarms. In these cases it is likely that each alarm is powered from a nearby power circuit that already existed, connected to different fuses, and the interlink wire can carry a live electric current to the other alarms around the building.

You may also notice a red light flashing roughly every 45 seconds on your alarm. Don't worry, this doesn't indicate a problem. This periodic flash simply indicates that the alarm has performed a self-test cycle and is a standard feature on these smoke alarms.

Ordinarily, it would only be possible to exchange a smoke alarm in this way for a new alarm of exactly the same model. However, the versatile 600 / 700 series from BRK can not only be replaced with a fresh detector head of the same model, but alarms with alkaline back-up batteries can often be upgraded to alarms with 10 year re-chargeable lithium backup battery (re-charged with constant trickle-charge). The key here is that the push-fit bases supplied with the 700MBX series smoke alarms are cross-compatible, and as such both the heads of the 600 series or the 700 series of BRK smoke detectors can be connected to your existing base fitting. However, the connector plug supplied with a 600MBX series alkaline alarm with twist base is not capable of re-charging the lithium battery of an MRL series alarm at this time, so alkaline MBX models must be purchased to replace these – please see the table below for the correct replacements for each model or click here for more information.

Before we make recommendations, which alarms can be replaced with what model, we need to explain the numbering system of BRK mains powered smoke alarms. Below, therefore is a graphic that explains what the part numbers of the 600 and 700 series BRK smoke alarms mean:


Please note that the bases, whether twist-on (6 as first digit) or click-on (7 as first digit) are fully interchangeable. It is also important to understand that when you receive your boxes with your new 600 or 700 series alarms, these are actually all containing a smoke alarm head that begins with the number 6, which sometimes leads to confusion! The differentiation between the 600 and 700 series, is, as hinted at above, just the different base. Here is what we will supply you with:

If you order for example BRK670MBX you receive:


If you order BRK770MRL you receive:


Replacement smoke alarms for BRK smoke alarms

Check the table below for the model of your existing smoke alarm to see which currently available smoke alarm is able to replace your alarm head.

Your old alarm Replacement alarm
660MBX 660MBX
660MRL 760MRL
760MBX 660MBX
or upgrade to 760MRL
760MRL 760MRL
670MBX 670MBX
670MRL 770MRL
770MBX 670MBX
or upgrade to 770MRL
770MRL 770MRL
690MBX 690MBX
690MRL 790MRL
790MBX 690MBX
or upgrade to 790MRL
790MRL 790MRL

All of the above replacement units are available from Safelincs with a best price guarantee, so don't delay and buy your replacement smoke alarms today! You can order online, email or ring 0800 612 6537.


Reviewed: 19/02/2019 (doc:313 V1.1). Our articles are reviewed regularly. However, any changes made to standards or legislation following the review date will not have been considered. Please note that we provide abridged, easy-to-understand guidance. To make detailed decisions about your fire safety provisions, you might require further advice or need to consult the full standards and legislation.