referring initially to fig1 , a personal alert safety system ( pass ) 10 is shown in use with a self - contained breathing apparatus ( scba ) 12 . as described herein , the pass 10 may be used with the scba 12 or independently , as necessary or desired . the scba 12 does not form part of the invention and is illustrated as an example of one form of an scba 12 . the pass 10 may be operable to detect firefighter motion , surrounding temperature , air pressure of scba cylinders , or the like . this application is not directed to these features , but rather a new method to manually start an emergency alarm . the scba 12 includes a high pressure air tank 14 providing breathable air in accordance with the en12021 standard . the scba 12 air is provided through a hose 16 to a mask 18 . the pass 10 is operatively connected to a pressure hose 20 also connected to the tank 14 . the pass 10 includes a housing 22 of generally parallelepiped construction including opposite insets 24 and 26 . the first inset 24 has a sound hole 25 . the first inset 24 also receives an adaptor 28 through which the pressure hose 20 passes . the second inset 26 also has a sound hole ( not shown ) and receives an activation key 30 . the sound holes open into the housing 22 and connect an internal tunnel for passing the audio alarm . a lens 31 between the insets 24 and 26 overlies an led 43 . as described below , the pass 10 is activated , i . e ., enabled for operation , responsive to the hose 20 being under pressure . in some instances , the pass 10 may be used without the pressure hose 20 and adaptor 28 , as shown in fig2 . in these instances , the activation key 30 must be removed to activate circuitry in the device . referring to fig3 , a block diagram illustrates an electronic circuit 32 contained on a circuit board within the housing 22 . the control circuit 32 includes a control 34 for controlling operation of the pass 10 . the control 34 may comprise a microcontroller including a processor and associated memory and operating in accordance with a control program for controlling operation of the pass 10 . the circuit 32 includes an accelerometer 36 having an output at terminals int 1 and int 2 connected to an interrupt input of the control 34 . the control 34 is also connected to a strain gauge 38 , a key detector block 40 , a speaker 42 and the led 43 . the speaker 42 may comprise , for example , a speaker and transducer functioning as a buzzer for generating an audio alarm that is dispersed through the sound holes 25 . the accelerometer 36 as described herein comprises a type adxl345 digital accelerometer . the accelerometer 36 is a low power device controlled by battery power from a power supply 44 . the accelerometer 36 measures dynamic acceleration resulting from pre - defined motion . particularly , tap sensing functionality is able to detect single and double taps in any direction . because the accelerometer 36 is fixedly mounted in the housing 22 , the accelerometer 36 is operable to sense tapping motion on the housing 22 . the accelerometer 36 is operated as illustrated in fig4 which compares acceleration to a threshold . the maximum tap duration time is defined by a value dur . a tap latency time is a waiting period from the end of a first tap until the start of a time window when a second tap can be detected . an interval after the latency time is defined by a window register . although a second tap must begin after a latency time has expired , the second tap does not have to finish before the end of the tap defined by the window register . the control circuit 32 can be used for either single tap operation or double tap operation although double tap is preferred to avoid inadvertent operation . a single tap interrupt is triggered when acceleration goes below the threshold as long as the duration dur has not been exceeded . a double tap interrupt is triggered when a second tap is sensed within the time window for the second tap . the control 34 is programmed to sense the interrupt from the accelerometer 36 and immediately initiate an alarm signal by providing a loud tone out the speaker 42 . a visual indication is provided by the led 43 . activation of the device and the alarm function are enabled by either the strain gauge 38 sensing a pressure condition from the high pressure hose 20 , in the configuration of fig1 , or by removal of the key 30 , in the configuration of fig2 , as sensed by the key detector block 40 . as described herein , manual initiation of an emergency alarm may be based on a double tap made on a specific axis with predetermined frequency and strength , as determined by the settings made in the accelerometer 36 . as a result , the pass 10 is easy to use with gloves and without sensitivity to how it is operated . the firefighter or other user need not search for a button in order to generate the alarm . moreover , the accelerometer 36 is not sensitive to electromagnetic fields or anti - static plastic and the pass 10 does not rely on buttons or the like which can wear out and require moving parts . in fact , there are fewer mechanical parts which can provide for faster assembly . this also results in lower manufacturing costs . it will be appreciated by those skilled in the art that there are many possible modifications to be made to the specific forms of the features and components of the disclosed embodiments while keeping within the spirit of the concepts disclosed herein . accordingly , no limitations to the specific forms of the embodiments disclosed herein should be read into the claims unless expressly recited in the claims . although a few embodiments have been described in detail above , other modifications are possible . other embodiments may be within the scope of the following claims .
a personal alert safety system comprises a housing adapted to be worn by a user . an accelerometer is in the housing . an alarm device is operatively associated with the housing . a control in the housing is operatively connected to the accelerometer and the alarm device . the control is configured to operate the alarm device responsive to select acceleration movement of the housing sensed by the accelerometer .