I am creating a battery operated device using an 8051. I am taking suggestions as to the best way to handle low battery conditions. Do I put in a Microprocessor Supervisor with battery comparator? Or do I use nothing and just let the unit die. I would like it to tell the user that the batteries are low, but I am not sure how to do it. If I use a 5 volt regulator with 4 AA batteries (6V) then when do I set the trigger to tell me the batteries are low? If the voltage drops below 5 volts, the output of the regulator and the input (connection to battery) is the same. So what do I compare?

Hope this is not too confusing...