Monitor Line Current

Need some ideas…

Have a BBB with powercape safely shutting itself down when line current loss occurs. The unit is inside a case along with a 4g modem and a switch that run off of a 24vdc psu, and the beagle runs off a 5vdc psu from the same line.

Goal: I would like to add a UPS to the entire unit that keeps the 4g router and switch powered so that the unit can sms text me in the case of a power loss. In order to do this I must some how monitor the incoming line current with the beagle.

Any suggestions? I was looking at the various current sensors that are available, the split core transformers seem sketchy…I thought maybe I could use a NC relay and just hold it open with power. Has anyone tried to do something like this?