Delta's Touch Sensitive Faucet does one thing and one thing well: It dispenses water when touched with any part of your body, then shuts off when touched again. Not only that, it's also a pretty fantastic faucet.
$547 on Delta's site, but $300ish if you shop around
This is a high quality faucet, even without the touch features, and most likely beats whatever faucet you have installed in your house when you built/bought it. Add the touch features to that, and you get the first true revolution in sink faucets that I've seen in a while.
This actually isn't Delta's first touch-sensitive faucet. They had one model before that had this feature plus a motion-sensitivity, and discovered that most people only used the touch-sensitivity and decided to focus there instead.
It's a little bit of a hassle to install, because you actually have to follow a series of instructions that has you removing your old faucet and installing this one (with the electronics that controls the touch-sensitivity). You actually need two people at one point, when you want to make sure you align the faucet correctly above the sink while the person below tightens.
It's not completely undoable if you have a spare hand and you're somewhat knowledgeable with tools, but I had a Delta professional install it to ensure optimum performance, and it didn't take too much longer than an hour.
The touch sensitivity, if installed correctly, is good, but not overly sensitive. The faucet and water handle, on the right, are both smart enough to detect the difference between a grasp—when you're moving the thing around—and a tap—when you're turning it on and off.
You turn on the faucet like any other faucet, by using the handle and switching it left for hot and right for cold. Once it's "on", you can tap anywhere on the body or the handle to turn it off. Tap it again to turn it back on. When you're completely done with washing, pull the handle down to the off position to ensure that a cat or a jumping baby brushing past it doesn't activate the water flow. It's also got a 4-minute timeout, so even if you do forget to turn the thing off, an accidental activation won't flood your house.
It's pretty great as an actual faucet too. The head has a pull-down for spray flexibility, and you can adjust the type of spray (like a shower) in one of two modes.
Warnings and Usage
If you install it yourself, make sure you install the base plate insulation unit, because if you don't, you're going to get finicky performance from the touch-sensitivity part. I had to have the installer revisit a couple times because it's not so clear in the instructions that many sinks need it, so even if you think you don't, put it in. Not doing so will make the touch only work 1 out of 3 or 4 times, which is a painful grey zone between not working at all, which is fine, and working all the time. If something like this happens to you, you can luckily disable the touch portion and just use it as a regular faucet until you get around to repairing it.
Also, be aware that you're going to get false positives occasionally when you're reaching over and grabbing something off your sink and you brush against the faucet. This is much less frustrating than the alternative of the thing NOT working when you want it to.
Is this practical?
Perhaps. You use your sink every day, but it's not that often that your hands are salmonella-tained enough to not be able to touch the handle and turn on the water manually. This is for those times. It's definitely a fantastic faucet, don't get me wrong, but it's a luxury. If you install this yourself without hiring a person to do so, $300 isn't too much to pay for the ability to turn something on with a touch. At my house, every guest that's seen it has been impressed. [Delta]
Touch works well, and allows you to turn it on with your arm, face or foot—whatever is currently less dirty than your hand
Works well as a faucet even without the touch technology
A little pricey, but not absurdly expensive
Installation might be tricky if you're not handy, and make sure you install the insulation plate, or you'll have sensitivity issues