A little - 1uA max when open, and up to 5V/20K = 250uA when closed, but could be as low as 5V/50K = 100uA.
Actually, it's simple.Just offset the reed switch so that as you open the mailbox, the magnet passes the reed switch, but does not activate it when fully closed.
Or, just turn off the pull-up while the switch is closed. (Requires polling to know when the switch is opened.)
Hmm great idea! So if I add magnet to extension arm, it will move inside mailbox past sensor, is that what you mean?
EDIT: Just found this education article on Sparkfun about pull-up resistor values. So 1 M resistor might be too big for ATmega to register key-press?
I know this is a super old thread, but maybe someone will find it via Google and this will help. I am sort of pursuing this same goal, using a reed switch to wake up a pro mini.I found a magnetic switch that has both NO and NC contacts. They are made by Sentrol and several other Home Automation / Alarm brands. They are sold as SPDT magnetic contacts. The part number for mine is 1076C. Hope this helps someone!!!