Detecting Low battery voltage

Hello everybody,
I am powering with Panda with a 9V battery (6LR61).
I want to create an alarm to detect low battery voltage.
Do you know a simple way to do this with a Panda?
Thanks in advance!

Take 9V, divide through a resistor divider network (2 resistors) and give the scaled down value to analog input on FEZ.

9V battery and 3V input limit on analog input is 1/3 ratio…
100K resistor and 200K is what you need. Voltage divider - Wikipedia

Looks easy.
Thanks Gus!