With only one LED indicator and one tact switch control, the device interface is designed for simplicity as follows. 1) Long press of the tact switch (3seconds) toggles the device onloffstatus. Walk and Exercise operation modes are selected when device is turned on. When the sensor is attached, the device will be turned on to Walk Mode. When the sensor is not attached, the device will be turned on to Exercise Mode. 2) Short press of the tact switch «3 seconds) rotates the stimulation intensity from level 1 st to 5th, and rotate back. This control can be executed only while the device is turned on.