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Fire Angel CO-9D Carbon Monoxide Detector Teardown

Fire Angel CO-9D CO Detector
Fire Angel CO-9D CO Detector

This detector has now been retired from service since it’s a fair bit out of date. So here’s the teardown!

Information
Information

Unlike older detectors, this unit has a built in battery that never needs replacing during the life of the sensor, so once the unit reaches it’s expiry date it’s just trashed as a whole.

Cover Removed
Cover Removed

4 screws hold the cover on, here’s the internals of the detector. There’s a 3v CR123A LiMnO² cell at the right for power, rated at 1500mAh. A 7 year life is quite remarkable on a single cell!
The sensor is just to the left of the lithium cell, and is of quite unusual construction. Previous CO sensor cells I’ve seen have been small cylinders with a pair of brass pins. This one appears to use a conductive plastic as the connections. These sensors contain H²SO⁴ so they’re a bit hazardous to open.
There are no manufacturer markings on the sensor & I’ve not been able to find any similarly shaped devices, so I’m unsure of it’s specifications.
The alarm sounder is on the left, the usual Piezo disc with a resonator to increase the loudness.

Microcontroller
Microcontroller

The brains of the device are provided by a Microchip PIC16F914 microcontroller. This is a fairly advanced device, with many onboard features, and NanoWatt™ technology, standby power consumption is <100nA according to Microchip’s Datasheet. This would explain the incredible battery life.
The choke just at the right edge of the photo is actually a transformer to drive the Piezo sounder at high voltage.

PCB Reverse
PCB Reverse

Here’s the PCB with the LCD frame removed. Not much to see on the this side, the silence/test button top right & the front end for the sensor.

Sensor Front End Amplifier
Sensor Front End Amplifier

Here’s a closer look at the front end for the CO sensor cell itself. I haven’t been able to decode the SMT markings on the SOT packages, but I’m guessing that there’s a pair of OpAmps & a voltage reference.

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Kidde Smoke Alarm

Top
Top

Old type ionization smoke alarm. Top of the device with the test button & sounder.

Bottom
Bottom

Bottom of the device. Battery compartment in centre.

PCB
PCB

Internals of the smoke alarm. Main component visible is the Ionization chamber.

Sounder
Sounder

Piezo sounder on inside of the top.

Ionization Chamber
Ionization Chamber

Inside the Ionization Chamber. 1µCi Americium-241 alpha particle source in the centre.
The radiation passes through the chamber, between the pair of electrodes, ionizing the air & permitting a small current to pass between the electrodes.
Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and interrupts this current, setting off the alarm.

Controller
Controller

Controller IC beneath the chamber.

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Window Break Alarm

Front
Front

Cheap unbranded window break alarm. Here is the front of the unit, with the sounder at the top, Power/sensitivity switch at the right. Battery test button at the left.

Rear
Rear

Rear of the device, with the adhesive pad used to attach it to a window.

Internals
Internals

Front cover removed, showing the batteries, PCB & the sounder.

PCB
PCB

PCB removed from the casing, showing the remaining components.