Jim... the only two things I can think of is 1) the battery (the inplanted
one) is getting to a point that it needs to be replaced; or 2) you are getting
near and/or around a sensing device such as the ones used for security measures
at airports and department stores that causes it to shut down.
I was told when mine was put in, to watch out for that such thing.
I really can't say for certain that either of these are absolute, but
hopefully this will open up a few ideas for you.
Steve


[Non-text portions of this message have been removed]