Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: There is a lock icon on the screen and I can't operate any functions. Does anyone know how to unlock?
Document: Can you set this to beep every 30 seconds for 10 minutes? If you can't does anyone know where I can find one like that?
Very useful. Always wanted a reliable timer and stopwatch, and here it is! I would recommend this item for just about anyone who can't wake up in the morning.
These are nitpicks though I'd be willing to pay an additional $5 for these functions. It's a good unit for the price.12-14-12 Update: Just bought another one of these in white. It is functionally different than the black one I have. Slightly different styling/cutaways for the keys in the front. Not quite as confusing to tell which numbers go with which buttons. Also, it has a lock switch on the side and the keys seem more difficult to push.
One of my favorite functions is the backward timing function. When the timer goes off, it automatically keeps track of how long it has been since the timer has gone off so you'll know how much time has elapsed. This is especially great for when you need to know the exact time frame for your particular oven for a particular dish, especially if it differs from the recipe instructions. I have three of these and it will now be my go-to timer of choice!
When I received this item, the clock function did not work well. Twenty-four hours after setting the clock to the correct time, the clock would be off by 5 hours. Because I loved having a timer I could wear around my neck, I kept the item. Bad decision. Just a few weeks later all functions of the unit stopped working and the screen went blank. I went and got a new battery and still the unit would not work.
The device works perfectly for clock, timer and count up (stopwatch) functions. The timer counts up after the preset time so you know how much over you are if you missed the bell. Great timer. The magnet is off center so the left hand side of the face tends to droop or swivel downward sometimes spontaneously, sometimes with the touch of use. I solved the problem to my satisfaction by attaching a tiny magnet to the back of the drooping side. Now, no worries mate.
It beeps each time you press a button and will continuously beep at a gradually faster speed, I think for about 1 minute if you don't push the stop button (haven't actually timed the length). After it stops beeping, it automatically goes into count up mode, so that when you do finally get to it, you know how much time has passed.I read one review where there was a complaint that you can't just button mash to stop the timer, and have to actually push stop.
Great timer for the price. I'm using it for many different things. Staying on task at work, watering trees in our yard, keeping our toddler in timeout, etc. The possibilities are endless. Time is money they say. I like the 0 through 9 dedicated keys to punch in the time. Makes it quick and easy. Ideas for improvement? 1. Add a lock button so keys can't be accidentally pushed 2. Add a mute button with some sort of blinking LED visual alarm  3.
I've bought many of these timers. My wife use it every day and more than once a day. So, I had to have the mine. It's very easy to operate and the battery lasts for long time. Excellent product.
Love this little time machine! It is easy to operate and accurate. I've finally STOPPED burning food since receiving the Polder Timer. I even use the Polder to time my exercise workouts!
Answer: The directions don't even mention LOCK feature.  Maybe try holding down the clear button for a few seconds?  Or try another battery?  Call them at 1-800-431-2133 toll free.