The BB Alert® Passive has been developed to provide the perfect harborage for bed bugs when they are not actively seeking a blood meal. During the majority of the time in a bed bugs life they are inactive and hiding, only coming out when seeking a blood meal. The BB Alert® Passive takes advantage of this biological fact and provides them with a harborage. As the bed bugs go into the harborage they excrete excess blood which can be seen by quick visual inspection on the white border around the unit.