An addon to all 9V battery fire alarms that sends the alarm and battery status to phones by Bluetooth. The phone then rings or sends a SMS.

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What if the alarm sounds when no-one is home, sleeping deep or is deaf. By connecting the fire alarm to the phone all those problem can be solved.

An addon between the 9V battery and the fire alarm to detect fire by measuring the power consumption of the unit. Also voltage measurement for low battery warning. A IoT microprocessor with Bluetooth Smart (4.1, Bluetooth low energy) will be used to send the alarm and warnings to a phone.

The phone can then let different apps respond to the message or vibrate to notify deaf. For example if the owner doesn't deactivate the alarm a SMS can be sent out to warn family and friends that the house is on fire. An app can also log the battery status and notify the user when he needs to buy a new battery.

An old phone can also be used as the bridge between the alarm and the internet to notify the user when he is on holidays.

A custom made minimal PCB and connector assembly that fits between the battery and the unit should be made.

Some basic requirements and functions:

  • Ultra low power
  • Small footprint to fit in existing devices
  • Minimal amount of components->use a SOC with everything needed built in
  • Beacon functions to know where the device is located
  • Prepared for mesh networks for multiple devices
  • Able to detect the difference between static, low battery warning and alarm power usage.
  • Wakeup on alarm to save power but still react to alarms
  • Notify user that battery change is needed when the voltage drops to low
  • more to come


  • Battery usage statistic and low battery warning systems for big IoT networks
  • Other user case where power consumption can be used as a sensor

Why Bluetooth?

To get IoT devices out on the Internet a low power protocol to WiFi/Cable converter is needed. 802.15.4 based protocols or 433MHz protocols are often used but not a lot of people has the converter at home. But almost everyone has a newer phone with BLE capability. Therefore the use of Bluetooth can simplify the connection to the world by using already available phones.

Other connected alarms:

There is a lot of mesh connected fire alarms on the market where the main function is to sound the alarm on all units in case of fire. Some of them can also be connected to home automation for more functionality. But the problem with those is that they requires more devices to be bought to enable more functions. Also there are often a higher price attached to those products compared to simple fire alarms.

The aim with this device is to connect existing fire alarms and add more functionality at a low price.

Status right now:

Ordered a TI CC2650 Launchpad for the prototyping.

Reading up on Eddystone Beacon, I think I will implement it as a connected Eddystone beacon,

Project plan:

  • Phase 1: Setting up a beacon with voltage, current, temperature and place information
  • Phase 2: Make some simple measurement on a fire alarm to get the characteristics of the power consumption.
  • Phase 2.5: Make a Android app to react(alarm and SMS/other service(Twitter?)) to an alarm based on the previous information (alarm, low battery warning).
  • Phase 3: Make a Settings app for changing things like the place of the beacon.
  • Phase 4: Find a smaller battery and make the first hardware design
  • Phase 5: Repeat to improve
  • Phase X: Add mesh/repeater functions, test different types of alarm makers, characteristic the power consumption to optimize the lifetime of the device, find other user cases like intrusion alarm, clocks and so on, add more to the battery log functions, add auto buy new battery.

  • Find the right SOC for the job

    Johan Westlund03/18/2016 at 18:05 0 comments

    I haven't looked at devices with propriety mesh protocols as I want it to be open and therefore devices that can be upgraded to the standard when it comes is a big plus. I have also been looking more for dual protocol chips so I don't lock my self to Bluetooth in case integration with home automation is needed where ZigBee has had more time to grow.

    Manufacturer ModelPriceAvg. powerConnectivityADCARCHComment
    TICC2650~$2.706.8µA(based on 2540)BLE, 802.15.4>5x12bit ARM M3+M0 for the communication Good support, probably BLE mesh in the future, Supports Over-the-Air updates, cheap dev kits
    Nordic SemiconductornRF51822~$2.315.6µABLE8x10bitARM M0
    NXPKW40Z~$2.06BLE, 802.15.41x16bit?ARM M0I like this one as well, but it have been hard to find information and the dev kits are a lot more expensiver


    For now the CC2650 looks hard to beat because of the more DIY approach and a lot of support and that from what I have found the only one that will work out of the box without additional ADC and compactors(I want the device to wake up in case of an alarm). This have been a half day research so if there is other SOCs and solutions, feel free to share. :)

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Johan Westlund wrote 03/20/2016 at 00:07 point

Just found this A WiFi 9V fire alarm battery. I'm happy that others have a similar idea. If you want this today, go ahead and buy one. I will probably will get one to compare the performance when this project nears the finish line.
PS. I got the idea before finding the roost. I still thinks there is a use for Bluetooth alarms so I will continue with this project. :)

  Are you sure? yes | no

hayden wrote 03/18/2016 at 09:40 point

nice idea, but your going to need a smaller custom battery to fit with your pcb in the standard battery spot ?

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Johan Westlund wrote 03/18/2016 at 13:50 point

From what I found a lot of 9V equipment has some extra space that I will try to use. Otherwise I'm thinking of other solutions like having wires going out to the side or that you remake the connector with the SmartAlarm integrated if you have this ones with a connector on a wire. I have to do some more research on different types of battery compartment in fire alarms to find this out. But for the prototype I will make it work in the fire alarm I have at home and that one has some extra space behind the battery.

But any suggestions of other solutions and places where you can get custom batteries are welcomed to contact me. :)

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hayden wrote 03/18/2016 at 21:15 point

yeah, often there lots of space inside them too, but i guess you dont
want to impede smoke ingress. i straight swap with existing 9v would be
good, as it would fit any model. maybe you have one made with lithium,
so it could have similar capacity to standard alkaline, and trade off
that capacity for size.

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hayden wrote 03/18/2016 at 21:18 point

  Are you sure? yes | no

Johan Westlund wrote 03/18/2016 at 22:04 point

Thanks for the link. I didn't mean to modify the detector, but there is some space in the battery compartment on some detectors. I didn't really want to have a special battery and enable the user to decide what battery to get, but to work in all detectors there probably needs to be a complete battery/SmartAlarm assembly. 

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