How can i tell if my guy has a penis implant?

Feels hard non-erect: Penis should be soft when it is flaccid. There is a condition called Peyronie's disease where men can have a hard plaque on top of penis under the skin. Penile implant goes full length of penis and never goes soft. Of course, you could always ask him. Penile implants are better than erectile dysfunction.

Permanently hard: Some are solid & flexible, others inflatable. Inflatable ones have pump control device in the scrotum which can be felt separate fro testicles. Penis with implant will never feel soft. Means he can perform ad infinitum!