LRI AW Photon LED Keychain Micro-Light, White BeamThis is the screwless back, push AND hold version. The one with the screws on the back has a slide switch on the front for locking the beam on. This one turns itself off the second you stop squeezing. LRI also makes an electronic switching version without a mechanical slide switch which will lock on by squeezing alone and includes brightness levels and a flashing mode.The cheapest is this push and hold version.Impressive light output and battery life. I used the slider version to hike out of Half Dome in Yosemite (from top to the Valley) in darkness the from Nevada Fall down to the Valley (NOT along the MIst Trail!). It provided plenty of light and the mechanical slider meant my thumb and finger didn't collapse from constant squeezing.This cheaper squeeze-only version has one outstanding feature besides much lower cost. It is really, really hard to kill the battery accidentally from accidental squeezing in the pocket, from coins, pocket knife, money clip etc., since even if some random pressure activates it, the moment the pressure is released the light turns back off - and constant accidental pressure is unlikely as stuff generally shifts around.Also, it is really really foolproof, I've had some problems with the slider edition.So - the electronically switching version can be turned on accidentally and drain itself. And the slider version is much more expensive, trickier to reassemble after battery change, and generally finicky.That leaves this as the king of emergency key chain lights that won't self-destruct.There's only one small, incredibly minor problem. It takes the harder to find 2016 batteries instead of the easier to find and often cheaper 2032 batteries. It needs dual 2016 batteries. Two 2016 batteries are as thick as one 2032 battery. The cheapest, easiest source of 2016's is Amazon Basics.Tip - if you DO use the 2032 battery, in this, in spare one or older one - you suddenly have a half-as-bright version which is neat for inflight use, where you don't wan't to wake up the whole cabin when you are trying to use the flashlight to find something. I often carry two together, the bright squeeze one with double 2016's and an older slider model with as single 2032 for reading.