Oops, that was a drawing error showing the garage sensor shorting to ground. It shorts the 5V to the input pin, which is also connected to the LED so I get visual confirmation that the Arduino knows the door is open.
I did, however, make an error in putting the 1k resistor with the relay coil. I checked the spec sheet on the relay (a cheapo from RadioShack, model 05P10), and it seems I don't need the resistor at all (5V / coil resistant of 56 Ohms = 89.3 mA current, listed as nominal coil current). I had it connected without a resistor on the breadboard on my bench and it was working fine. I added the resistor thinking that I might be putting too much current through the coil. Is that 89.3 mA current too much for the Arduino to put out? Like I said, it was working for me, but if that will be stressing the Arduino too much, I can always use a different relay (I have one that requires only 15-20 mA, http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110909482881&ssPageName=ADME:L:OC:US:3160, but I didn't want to waste 4 relays when I only need one).
I thought about adding a buzzer/alarm like you mentioned, but I didn't want to waste my only buzzer that came with my starter kit (I have a Mega on the way to replace my Uno once it's installed in the garage). I know what you mean about the garage door status. I considered adding a 2nd sensor to detect that the door closed, that way it doesn't assume it's closed if it's not completely opened. I was going to have it send me a message if it gets confused and the door is neither open nor closed, but I don't feel like running an Ethernet cable to the garage (and the WiFi shields are pricey!). I don't picture it being a problem often (if ever), and since the relay just drives the regular garage door operator contacts, it will still use the laser sights to prevent it from closing the door on something. I'll definitely consider adding that extra stuff in the future; right now I'd rather just get the thing installed and working.
My last thing to check is how much current is running through when I short the 2 pins for the garage door opener. My relay is rated for 1A at 120AC/24VDC, and I wouldn't think it's using more than that. Still, I'd rather check with the multimeter before I go and ruin my relay or start a fire!
Thanks for the feedback. Any other ideas?