I'm working on controlling my garage door (via 2n2222) and I checked the limit sensors on my Genie are 0/5v depending on whether the door is open or closed. Should I use something like a transistor to protect my Arduino from the voltage coming from the garage door sensor or can I just plug it straight into a digital pin?
Thanks!
Best to have an optocoupler in between, that prevents spikes to enter the Arduino.
How is the garage door powered?
Can you post some sort of schematic?
I'm very new to circuit design, so please be kind 
Here's what I was thinking for the door sensor, opener, temparture sensor (DS18B20), smoke detector, and PiR sensor:
UPDATE: Link to block diagram
picture link didn't work
My mistake. The link was updated in the reply above.
hi !
use a TLP621 as optocoupler to isolate incomming or outgoing signals from the arduino, ANYTIME
have a nice day