One of the most common bed bug monitors is a glueboard bent into a triangle. These devices are placed randomly in suites in the hopes of discovering bed bugs. The difficulty is that these devices only occupy a tiny percentage of the floor area in a suite so the chance that a bed bug would actually be caught is very small. Typically if I find a bed bug in one if these devices a 15 second inspection of the bed would tell the same story as the infestation is already then quite advanced. As such I do not find these devices to be very helpful. They are meant more as a public relations device. The tenant looks at the glueboard traps and finds no bugs. The tenant is therefore happy.
On the other hand if you use glueboards under a bed leg and ensure the bed is properly isolated the glueboards become excellent monitors. You can make your own bed leg glue board monitor by placing an empty tuna can in the middle of a mouse glueboard. Place the bed leg in the empty tuna can and it is the cheapest and most effective bed bug monitor on the market today.
An interesting story is applicable here. In one case I provided a tenant with these glue board monitors under the bed legs and the tenant decided that if 4 monitors under the bed legs were good it would be even better to place monitors under the legs of every piece of furniture she owned. As such there were about 30 or 40 furniture legs with glueboards under them in the suite when I returned for inspection. I found about a dozen bugs in the bed leg glue boards and zero bugs for the entire rest of the suite. Interesting.
There is one other place where the glue boards work well and that is in cases where climb up interceptors are being used with the bed shoved against the wall. The bugs are repelled from the interceptors and wander around under the bed looking for a better place to climb. If you place random glue boards under the bed in this setting they are also quite effective because the bugs are spending a lot of time wandering under the bed.