My Snuza Hero MD movement light flashes red and it beeps (like a low battery alert, but I have replaced the battery recently).

If no breathing movement has been detected for 15 seconds, the Hero will gently vibrate in an attempt to rouse your baby.  The Alarm Indicator Light flashes simultaneously.  When your Snuza Hero MD flashes red and you can hear the audible alarm, you need to immediately check on your baby.  This alert is activated when no breathing movement has been detected for 20 seconds.