Ultra low power configuration for a microcontroller switch?
If you want to "test" the state of a reed switch (open or closed) then drive it with (say) 10 uA from an IO line via a suitable resistor and read the signal coming back. Once read, turn off the driving signal. Keep duty cycle low to maintain &lt; 1uA average consumption.

Have the reed switch grounded on one pin and read back the state on the other pin (the junction of the reed switch and suitable resistor).

The "suitable resistor" might be between 10 kohm and 1 Mohm depending on the wetting current needed by the reed contact.