When using your device often, it is very common that the sensor needs to be reset if you are experiencing multiple count downs with no option to blow or unusual readings.  Please take out the batteries and leave to rest for 45-60 mins and try performing a test again.If the device continues to cycle the countdown or give out unusual readings, then it will require 24 hrs resting period and maybe brand new batteries.Please note that you should only be blowing into your device once every 5-7 minutes. Otherwise this can overload the sensor.