The house that I grew up in had an addition on a separate HVAC system than the rest of the house. Once we went on vacation for a week and closed the addition off (turned off the HVAC, etc). Our family dog had free run of the rest of the house while we were gone, but not the addition.
After a week without access to food, the fleas in the addition were RAVENOUS. I remember walking into the addition in white socks and my feet instantly had several dozen black dots on them.
If there are no longer pets in your home, I suspect any fleas that are present will soon start snacking on the humans (so if you have flea bites, you have fleas).
This won't tell you if you have eggs (or hibernating pupae). You can encourage adult fleas to emerge by increasing the room's temperature and humidity.