Difference between battery and PSU

Hello someone.

I have a small device I have put together from a small watch. It now says "beep" when the battery is connected. I want to couple it to an Atmega16 (MCU) so I can hear the beep when it restarts (by watchdog timer). The problem is: When I connect 1.5V battery it works fine, but if I make a voltage division from VCC 5V to get 1.5V to feed the thing it doesn't "beep". Why is that (not) happening?

Hope someone can help me!

Possibly you're using too high a value resistors?.

No, I have tried to connect it (shortly) to the 5V just to check, it didn't work with that either (and it still works after that with the battery)

Ok. Problem solved! If I Use a small diode in series with the thing it works! I guess it must be that the diode is limiting the current or something(?)..