How to test if a program was invoked by a console user?

I've built an application that emulates a HID device via /dev/uhid on linux. My application is broken into two programs. First, a very simple setuid root binary that opens /dev/uhid and emulates just the one device, passing messages back and forth to the program that invoked it. Second, an application that actually contains all of the device logic, and uses the other binary just to encapsulate uhid_event messages and talk to the kernel. Anyone with console access can plug in a hardware USB device anyway, but for security, I would like the setuid program to refuse to run on behalf of non-console users. My question: What's the simplest, most robust way for a setuid root application to check if it was invoked by a console user and bail if not, or to restrict execution of the program to console users in the first place?