Pros: Useful, simple installation, robust design, good performance.
Cons: Overly engineered for safety; non-intuitive button/beep sequences.
After constructing a new, detached garage, my wife and I found ourselves accidentally leaving our garage doors open. This is probably because we don't exit the garage from the side entry, but rather out the garage doors themselves. The AutoCloser from Xceltronix is the only device of its kind that I could find, without going into complex systems. At $52+s/h, the price was OK and I found several good reviews on-line.
Basically, the AutoCloser is a little box that velcros on to the bottom of your garage door opener and shoots a little beam at a reflector that you attach to the drive arm on your garage door. This way, the unit knows when your garge door opens, and it starts an internal countdown timer (from 5 to 20 minutes), and 30 sec before activating the door to close it, it emits a series of beeps. There is also a wall button that serves as a way to override/cancel the AutoCloser either before or after it starts is warning beeps. You can also just manually turn the device off.
I thought the detector beam and reflector alone sounded a little goofy, but it works quite well and the beam is sensitive enough that the target reflector doesn't have to be mounted perfectly - it detects it easily when positioned pretty much anywhere in front of it. The instructions indicate that it must be within 3 feet, but with most openers, the distance is more like 1 foot. The drive arm on the garage door opener usually has multiple holes (to aid in installation of the opener) - so there are usually extra holes for mounting the reflector. Mine had three possible positions, and I found that all three worked equally well, despite two of them being somewhat off-set.
The system is wired in parallel with your normal opener controls (and remote), so it doesn't affect how you normally use the door. Also, all the safety features of your door (object detection, auto-reverse, etc.) still function as normal.
I have only two small complaints. Firstly, when the AutoCloser kicks in (after the 5- to 20-minute programmed delay, and 30 seconds of beeping), it initially only closes the door about 20% and then goes back up. This is followed by a few more seconds of beeping and then the door goes all the way down. I assume this is a safety feature, helping let people know that the door is about to close. To me, I think the beeping is enough, but I suppose if you were inside your car in the driveway (or inside the garage with your stereo on), you might not be able to hear the beeping. Although, it you're inside the garage, you wouldn't see it go down anyway. Regardless, if your trip your garage door opener's normal safety photo eye detector - the door will reverse up as usual.
Second, the override button can be used in a couple different ways, and the unit sends out a series of beeps that are supposed to let you know when the unit is in override mode, etc. - but it's all too confusing and hard to remember how many beeps mean what, how many times you're suppose to press the button, etc. All you need to know is that, if the AutoCloser kicks in while you're in the garage, you have about 30 seconds to press the button twice to override it.
All in all, though, the system works well as it describes, and I'm ordering a 2nd one for our other garage door.