Title says it all:
Twice yesterday, when I started my car (both time it was locked), a big flashing error message said that the key remote was not present - but it was in my pocket both times. First time I restarted the car - second time, the error messge seemed to time out.

Is this a battery issue?

 

It happens to me occasionally, I changed the batteries, but it still does it. Taking it out of your pocket and placing somewhere else usually solves the problem.

 

Do you have it in the same pocket as your cell phone? I think there have been threads where people have stated that the cell phone interferes with the signal from the fob.

 

Sounds very reasonable to me, since I usually have the fob in my right pocket and my cell phone is always in the center console plugged in.