Remove the battery and press the ON/OFF button while the battery is out. Place the battery back into the Snuza Hero. Do not switch the unit ON. Does the Snuza Hero MD start alarming with the battery light flashing red? If yes, Replace the battery if the Snuza Hero MD has been used extensively for a long period of time. If the battery has recently been replaced contact a Representative if the Hero is still under the 12 month guarantee. Go to contact us page and complete the form on the website.