When inspecting a suite for bed bugs the most important place to look is on sleeping surfaces. Any bug imported into the suite, especially in small infestations, inevitably ends up there. How do they do that? We don’t know.
We know that Co2 is a primary driver with Robert Usinger suggesting the bugs can home in on that source from about 5 feet. Also heat is an attractant with bugs able to sense heat from about 1 foot. Studies showed the actual temperature was not as important as the difference in temperature. Also various smells a human emits attracts bed bugs but these are less important that heat and Co2. For example a smelly sock in a climb up interceptor will catch more bugs than a random interceptor.
I have noted that bed bugs can accurately find their host from a distance of 20 or 30 feet. In one case a man self treated his suite with copious amounts of pyrodust except for a stuffed chair in an unused room. The bugs were repelled from the pyrodust and harboured in the stuffed chair 25 feet away from the bed. Every day the bugs would march the 25 feet to get their blood meal. Interestingly enough the suite directly across the hall was bug free despite this daily ritual suggesting the bugs did not get lost – they knew where they were going.
I think sometimes we underestimate the bed bug. A one millimetre tall bed bug is looking for a host 6 feet tall and weighs, in comparison, a massive amount. In comparison we might ask ourselves if a human could find a giant as tall as the empire state building with only limited senses. I think the vibrations alone caused by an empire state sized giant would be very easy to follow. When that giant made a noise it would be equivalent of a freight train in our ears. Perhaps the bugs are following simple cues like these.
Another method might involve the aggressive nature of the bed bug. Bed bugs are known to feed opportunistically and will climb onto a nearby person during the day. For example I recently treated a home where a recent funeral gathering had taken place. A man known to be severely infested with bed bugs was present and sat in one of the stuffed chairs. 5 days later the home owner noted a bed bug climbing on her arm as she sat in that same stuffed chair. The home was treated and no other sign of bugs was noted. Given bugs are clumsy when walking down it is possible that this bed bug might stay on the clothes for several hours and get a ride up to the bedroom at bed time. When the clothing is removed the bug climbs off and has perfect access to a night time meal.
We do not know exactly how the bed bug finds its host. Maybe their methods are quite simple.