Microchips such as BackHome BioGlass mini transponders can be used to electronically identify horses just as easily as they are used to identify dogs and cats.
To scan for them you need to know where the microchip is placed.
In the horse, there are two recognised implantation sites currently in use:
Feramo® with Chromium
Intracillin® 300 Injection
Sedazine A.C.P.® Paste