The Lock out can be challenging due to the description in the manual. The procedure is to do a single click, a double click and then a triple click all in less than around 5 seconds- and it can't just be 6 clicks, there has to be a micro pause between the one click, two click and three click. For some reason it seems a lot easier to me to get it locked than unlocked. And taking the battery out does not change anything. To balance my negativity regarding the lockout, I must say I LOVE this little light(OK, I bought three, one black, one gray and one red). It is one of the most favored AAA light in my collection(I have around 50 AAA lights, as they are always part of my backup, but at home they are often the light of choice for night time prowling around the house. My very first E02 died after a drop of 3 feet. Fortunately Manker provides excellent customer service-they had a new one in the mail to me within 48 hours and did not have me send the dead one back. Please let me know if the above sequence solves the issue, it took me a while to get the timing down. BTW, when locking it out, after mastering the 1,2,3 clicks, it will illuminate in an incredibly dim "moonlight" mode for 5 seconds and then turn off. When it unlocks, it comes on in medium for me most the time. Good Luck!