The automatic models are neat because they are actually able to sense when your hands are cocked under the device. It can do this by a LED sensor light that can detect when there is movement under the nozzle. Users will have to employ the use of sometimes up to 5 batteries to get their device up and running. While many models have a gauge at the top to allow users to adjust the amount of suds that are dispersed in a single swipe, some devices will actually continue to pump out liquid as long as it detects that there are hands under the nozzle.