You're sounding like "Tim the tool man Taylor.....". "More power".......

You can run almost anything electric from almost any source provided.....

-Input voltage is ~correct (or within range)
-Voltage type (AC or DC)
Current supply is at least the minimum required

Could you run a ~3VDC device off a 12VDC supply?...... sure, provided it can supply the required amps and you step the voltage down.
Heck, you can run a 3VDC device from a 440VAC 1000A supply if you drop the voltage (a lot) and run a rectifier to make it DC.

For a remote car FOB, just use the correct frikkin coin battery.>:laugh::wink2::nerd2:

 

Thanks.
Fresh battery it is for now. Should last me a good long time.

However, I also got another answer leaning more to the technical answer that I should have been more clear in asking for. How do physically, electrically adapt it.

"You can use a standard USB charger (5V) with three silicon power diodes (1N4001, etc.) in series to drop the voltage down to 3V. Be sure to put the diodes in the correct polarity direction (cathodes towards negative)."

 

That would work, but since the current draw of the remote is so low it would be better to just scrap the 5V supply and use a 3V zener.

 

Maybe you could link to a product so I can do my home work? I would love not to waste space/ money

 

Personally I'd opt to just use a battery like CHARLIEIII stated and just use a purchased socket like linked below...
https://www.amazon.com/gp/aw/d/B00MNGCDVS/ref=ox_sc_saved_image_8?ie=UTF8&psc=1&smid=A2JE1V94UJXPY3

But...sometimes it's fun to play with electronics and see what you can do.

You could try a premade dc to dc converter or make your own if you want to do some soldering on a perf board.

http://www.amazon.com/gp/aw/d/B00C0...-1&pi=SY200_QL40&keywords=dc+to+dc+converter&dpPl=1&dpID=41H+uMU-HWL&ref=plSrch

https://youtu.be/GSzVs7_aW-Y

 

OK, I'll bite, why do you want to hardwire the FOB? Wouldn't it be better to be portable? If portable, then any "solution" would greatly increase it's size making it less portable, sorta defeats the purpose.

 

Thanks @reko I might go with that someday. The vid is good info.



It's part of my remote starter install, to keep stock alarm functionality.
OEM Keyfob is going to live in the dash, wired to the remote starter's door lock/unlock wires.
This alleviates needing to carry 2 keyfobs, wiring into the car for door locks, and having to change the battery (if I hardwire the power). So portability is a moot point.

One of 2 relays is shown.

 

You could also use a 3.3V linear regulator. A switching type supply (usb power adapter) would be a poor choice for this application. The idle current draw of the adapter could be a few hundred mA depending on the adapter design. They also tend to have quite a bit of high frequency ripple on the output that could have an affect on the remotes function since it was designed to be battery powered.

 

Much appreciated man. Sounds good.
I'll whip up something like this:

with these: