im looking to monitor a UPS ( 12v 12 Amp output) via photon
is there any firmware build?
thanks
Can you explain how you would like to monitor it? Do you just need to determine if 12VDC is present or not? Are you looking to monitor the current being drawn from the UPS? Are you looking to monitor the exact output voltage of the UPS(0-12VDC)?
I want to hack the Ups before the inverter and use 12v to backup my home alarm
it has 2 batteries 12v 7.2 AH each
I want to monitor the 12V output
Do you want to monitor the level of the 12VDC or do you just want to know if it is 0 or 12VDC?
Im not sure, 
, what is the best info needed to know status of your backup power?
The easiest is Battery Voltage.
The UPS will likely maintain the battery on a Float Charge during no demand.
Just monitor the Battery Voltage and approximate the % Charge
For instance, a UPS using a SLA battery has lost power and is using the battery backup when the voltage drops below 12.7 Volts
I would agree with @rfontaine. I think one of these products would work best for your application:
https://store.ncd.io/?post_type=product&s=0-20&site_select=https%3A%2F%2Fstore.ncd.io%3Fpost_type%3Dproduct&fwp_main_facet=iot-devices&fwp_adc_voltage=0-20v
They have 0-20VDC inputs so they should have no trouble with your 0-13VDCish voltage monitoring. The ADCs on these boards are 12 Bit so that should give you a reading resolution of around 0.0045VDC. They can also be monitored in 16 bit which gives you even higher resolution but that is probably overkill for this application.
great info, thanks
i need a custom firmware correct?
You will need firmware on the Photon that monitors that voltage level and then in some way presents it to you for monitoring, so yes, custom firmware will be required.