Hey all i am looking for some advice in how to go about my project with a Nest Protect gen 2.

In my home i have ran cat6 wire to all 3 locations that require a smoke detector. These cat6 cables are connected to a POE switch for powering the Nest Protect.

The version i picked up for the Nest Protect is the battery version. I am wanting to convert the battery to the POE in order to power it by POE instead of battery. The Nest Protect uses 6 x AA batteries that equal ~9vdc total.

enter image description here

I am converting the POE to 9vdc via a converter:

enter image description here

However my question is- do I need to wire up the 6 battery placers in parallel or series? It would seem that the Nest Protect AC version has only 3 x AA for power backup. Not sure if that matters in my case or not.

  • 1
    \$\begingroup\$ Also you realise this gives you no power redundancy, meaning that your smoke detector will stop working if you have a power cut in the middle of the night and smoke fills your house and you die... \$\endgroup\$
    – BeB00
    Jul 9, 2018 at 19:16
  • \$\begingroup\$ @beB00 the Poe is on a battery backup. \$\endgroup\$
    – StealthRT
    Jul 9, 2018 at 19:18
  • 2
    \$\begingroup\$ Thats better, but I would still be wary of having a lifesaving device relying on a power source nowhere near it. There's a reason that the POE version has batteries as well \$\endgroup\$
    – BeB00
    Jul 9, 2018 at 19:19
  • \$\begingroup\$ @BeB00 You mean the AC version has the 3 batteries for backup. There is no POE version of the Nest Protect Gen 2. \$\endgroup\$
    – StealthRT
    Jul 9, 2018 at 19:30
  • \$\begingroup\$ yup thats what i mean \$\endgroup\$
    – BeB00
    Jul 9, 2018 at 23:20

1 Answer 1


You should find and measure the battery string voltage then jumper +,- to the ends. It is unlikely (yet possible) that middle battery connections are used. They should not be jumpered.

If this assumption is untrue, then a virtual ground buffer must be added to split the supply to +/-4.5V such as possibly leaving the batteries in place with the 9.0V applied with a series R.

A DMM resistance check with each battery terminal to the PCB will tell you if the intermediate terminals are used.

Stack Jacks could combine 1 supply to all remotes if hardwired.

  • \$\begingroup\$ That was my question - if the AC version has 3 batteries for its backup then maybe only 3 batteries are being used in the Battery version as well and have the other 3 batteries as its backup? \$\endgroup\$
    – StealthRT
    Jul 9, 2018 at 19:32
  • \$\begingroup\$ If you look at the Nest Protect image I posted then you may see that the left side batteries are all pointing the same way - that being Negative to Positive while the batteries on the right side are Positive to Negative. \$\endgroup\$
    – StealthRT
    Jul 9, 2018 at 19:33
  • \$\begingroup\$ There also seems to be 2 wires each coming out from the left side bundle of 3 batteries and 2 wires coming out from the right side bundle of 3 batteries. \$\endgroup\$
    – StealthRT
    Jul 9, 2018 at 19:35
  • \$\begingroup\$ insufficient clues. You must ohm out the wiring to be sure how the batteries voltages are used and make schematic. \$\endgroup\$ Jul 9, 2018 at 19:39

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