Fall detection devices detect when a person falls. FIG. 1 shows a system device worn on a person that uses an accelerometer, barometer, microprocessor, and wireless transmitter to detect falls. Such a device, typically part of a mobile personal emergency response system (“MPERS”), can be placed in particular positions on the body (such as: pendant, shirt pocket, wrist, and on the waist) to sense movement based on signals from the accelerometer and changes in relative barometric pressure signals to determine if a person has fallen. The MPERS device can transmit medical and health information of the wearer to a central host computer server that can route the information to an emergency response provider. An approach to reduce the number of false positive indications within fall detection devices that use a barometer and accelerometer is described. The accelerometer senses changes in acceleration to facilitate characterization of orientation, movement, and impact associated with a current movement event that may be a fall event. A barometer senses relative pressure of the surroundings and can indicate a device's level relative to the ground by correlating the lower pressure present at higher distances above the ground and higher pressure when closer to the ground. The microprocessor processes the barometric, and accelerometer information to make inferences on if a fall has occurred. The wireless transmitter can transmit a message to a base station connected to a wired connection, or a wireless connection, for example a long range wireless link such as cellular telephony or cellular modem, or a short range wireless link such as Wi-Fi, Bluetooth, RFID, and the like to indicate and/or transmit a message to notify and to request help when the microprocessor determines a person wearing the MPERS device has fallen. The host computer can also process the received message to determine whether help is needed by a wearer. The processing can include performing various algorithms.
Shown in FIG. 2 is the 3-axis (X,Y,Z) accelerometer data taken for a typical fall with a pendant device. Fall detection devices can detect if a fall has occurred by sensing a large change in acceleration. But, determining the differences between falls and other events such as drops or sits, which an MPERS device may erroneously interpret as a fall event (i.e., the non-fall events interpreted as fall events are “false positives”) can present difficulty to an MPERS device. A detailed and scientific way of understanding the differences between a fall event and a false positive can facilitate improved determination of, and distinguishing between, an actual fall event and a non-fall event, or a false positive.
When a fall occurs, the barometric pressure increases from when the person was standing to when the person is on the ground. FIG. 3 shows the increase in barometric pressure for a typical fall indicating that the device is more than 3.5 feet above the ground and then is on the ground after a fall event, based on the pressure before and after the fall event.