Disclosed is a technique for passively monitoring the number of guests in a rental property. Mobile device broadcasts intended for connecting the device to a wireless network contain information about that device. This information includes unique identifiers such as MAC addresses. Detecting these broadcasts and filtering out those devices that are expected enables a property owner to have a semi-accurate number of guests within their property without actually being at the property, or visibly observing the guests in an obtrusive fashion. Guests are able to enjoy themselves in privacy and the property owner is able to monitor the safety of their property.