Building security systems are commonly deployed to detect intrusion and burglary in home and business structures. Such systems can accurately detect door open/close events, but their high-cost of installation and maintenance makes them unsuitable for certain building monitoring applications, such as times of high/low entrance traffic, estimating building occupancy, etc.

In this paper, we show that barometer sensors found in latest smartphones can directly detect the building door open/close events anywhere inside an insulated building. The sudden pressure change observed by barometers is sufficient to detect events even in presence of user mobility (e.g. climbing stairs). We study various characteristics of the pressure variation due to door events, and demonstrate that door open/close events can be recognized with an accuracy range of 99.34% - 99.81% based on the data collected from 3 different buildings. Such a low-cost ubiquitous solution of door event detection enables many monitoring applications without any infrastructure integration, and it can also work as an augmentation to the existing expensive security systems.

Building security systems have become commonplace for protecting against intrusions and burglary in homes, offices and businesses. Currently, most prevalent form of building security system requires installing an electrical circuit on the periphery of doors to detect their open/close events. However, due to their high cost, these building security systems are undesirable for many simple monitoring applications, such as logging door open/close events, estimating building occupancy, times of high/low entrance traffic, etc. In fact, these needs of monitoring building door open/close events can be fulfilled with a barometer sensor in a latest smartphone, which requires no infrastructure integration.

In this paper, we provide an empirical evidence that the barometer sensor commonly found in latest smartphones can directly detect the building door open/close events anywhere inside an insulated building. This observation is based on the fact that most of the buildings are equipped with HVAC(Heating, Ventilating and Air Conditioning) systems to maintain a convenient indoor temperature and pressure. It uses a compressor to eject/absorb the air to/from the outside for ventilation, which creates a noticeable pressure difference between the indoor and outdoor environment. When a building door is opened, the sharp change of indoor pressure can be easily observed using smartphone barometer sensors. Once the door is closed, the HVAC system restores the pressure level allowing the detection of next open/close event.