ACR recommends briefly testing your 400 every 6 months at a minimum. To test: Take the device outdoors with a clear view of the sky, Hold vertically with antenna pointed up, Press and hold the button for 1 second (do not let go), The strobe will start blinking to confirm test signal sent, Release button after test completion. Keep in mind that testing too frequently can drain the battery. Also never test indoors as it may actually transmit the distress signal.