I have been trying to search for information on the component of a fire alarm that sounds the siren. My goal is to remove the siren and use the power and ground to connect to an arduino. I want the arduino to be alerted instead of sounding the alarm. The component has 3 prongs that are soldered into the board and I cannot figure out what each one does. Pictures are below:

Note: No this alarm will not be used as a normal fire alarm in a life or death situation.

top of board

bottom of board

  • \$\begingroup\$ Correct it is S2. I will get the other info soon. \$\endgroup\$
    – rys
    Feb 13, 2015 at 5:37
  • \$\begingroup\$ I will get the photo replaced. I do not know the function for LED1. It was always empty. What number do I use on the DIP-16 IC? There are 3 numbers: A5366CAT, 1428824R, INDO. \$\endgroup\$
    – rys
    Feb 13, 2015 at 5:53
  • \$\begingroup\$ No need, I think! The datasheet knows all! :D \$\endgroup\$
    – Jon
    Feb 13, 2015 at 6:07

2 Answers 2


A5366: Photoelectric Smoke Detector with Interconnect and Timer


pin 7 is I/O Pin : A connection at this pin allows multiple smoke detectors to be interconnected. If any single unit detects smoke, its I/O pin is driven high, and all connected units will sound their associated horns.

The above data sheet has a nice typical circuit. Likely just what you have there. The Horn appears to be a 3 pin Piezo. Where its feed back and pulsing will not be as easy, as just monitoring pin 7 of the chip.

Be-warned: this chip runs directly off of battery, up to 15V. Typically 9V battery. So the output of the IO will be that to. So it would be best to drive a resistor divider or clamping diode or something to ensure it does not exceed the VCC of the Arduino.

here is an example circuit to protect against the higher voltage of the A5366.


simulate this circuit – Schematic created using CircuitLab

D2 is optional. BAV99 is a nice little SOT23 that can do this.

  • \$\begingroup\$ Yeah, what HE said. \$\endgroup\$
    – Jon
    Feb 13, 2015 at 6:10
  • \$\begingroup\$ ha :) thank you both. I'll check an answer after I have time to test it out. \$\endgroup\$
    – rys
    Feb 13, 2015 at 6:11
  • \$\begingroup\$ Why was this down voted? Is something incorrect? \$\endgroup\$
    – rys
    Feb 16, 2015 at 18:48
  • \$\begingroup\$ So you just simply added a 10K resistor to lower voltage correct? \$\endgroup\$
    – rys
    Feb 16, 2015 at 20:04
  • \$\begingroup\$ D1 prevents the voltage at AVRinput exceeding AVRvcc, likewise D2 prevents it from going below the AVR's ground. The difference is dissipated across the 10K. Choose a R of your liking. This technique is used to protect most things. Most all chips have these diodes on all pins. But they are only strong enough to take minor static spikes. Hence in this case it is prudent to add stronger one and a resistor to absorb the diff. (not sure why someone down ticked it.) \$\endgroup\$
    – mpflaga
    Feb 16, 2015 at 21:26

With the IC part number, I was able to find this for you:

The "typical application diagram" should be able to help you considerably, even if I am not.

Pin 7 is I/O interconnect:
When driven high by the Arduino, the alarm will sound. When read by the Arduino, a HIGH signal indicates the alarm is going off.

Pin 11 is LED output and flashes to indicate the current status:
Standby - Every 43s
Local Smoke - Every 0.5s
Remote Alarm - No pulses
Test Mode - Every 0.5s
Timer Mode - Every 10s

You should certainly be able to detect those with an Arduino.

  • \$\begingroup\$ Wow, that is very helpful. I will try this out and let you know. \$\endgroup\$
    – rys
    Feb 13, 2015 at 6:07
  • \$\begingroup\$ Pin 7 is your best bet; it is used to make multiple detectors all go off together when any one of them goes off. I suspect that pin is routed to CONN1. \$\endgroup\$
    – Jon
    Feb 13, 2015 at 6:08
  • \$\begingroup\$ You got lucky, I up voted but can't down vote yet lol. \$\endgroup\$
    – rys
    Feb 17, 2015 at 23:26
  • \$\begingroup\$ You can up-vote again to remove it \$\endgroup\$
    – Jon
    Feb 18, 2015 at 0:18

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