Henrik,

I don't have a spec sheet for the reed switch so I can't verify the current capacity but it is rather small (~5mm l. reeds) in glass tube. The pullups are 47k ohm and on the control board about 8mm away from the pic Ports C4-C6 and connect with a ground trace which incidentally shares the same trace with Vss two pins away. I have the usual bypass cap (100nf) soldered across the Vss & Vdd pins directly below the PIC.

I understand what you suggest about too weak a pullup, I had wondered about that myself, but I am unsure of how high a pullup current the pin should see, in other words how "stiff" the pullup should be. The spec sheet says the source current max on any port pin is 25mA. My gut tells me the reed switch should be able to handle that at 5vDC but I would hope that it would not be necessary to max out the current to mask the noise.

Any thoughts?