Kitchen timers can certainly be a great tool in the home for helping you watch items that are cooking while dealing with all the other distractions that maintaining a household brings. There are tons of kitchen timers out in the market with just as many features.
The very basic of cooking timers comes from the process of timing an egg to perfection. The proverbial three minute egg may be too hard for your tastes. The first to hit the markets were the hour glass style where a glass vial that is very thin in the middle, larger on either end holds sand. You turn the vial over and when the sand drains into the other side timing for three minutes. You have to watch the timer or you will over cook the egg. The three minute egg timer is for soft boiled eggs and you will need to adjust accordingly if you like them hard boiled.
Next in our race to make a better timer comes the manual windup styles where you turn a knob to the correct time you want and it works like a countdown timer going from the highest to zero. When it gets to the zero on the timer a bell or some other sound will ring or a buzz letting you know you have reached the desired time. This was a great step forward as you do not have to be in the kitchen watching both the item you are cooking and the timer. These kitchen timers are pretty accurate and very reliable. They are constructed well and have a simple design. They are still widely used today.
Enter the digital age of computers and electronics. There are a plethora of digital electronic kitchen timers on the market. Most of these electronic timers multitask and at the basic model has a timer along with a stop watch. Some have thermometers that you can plug in so that timing along with temperature of meat items can be used to cook that roast perfectly. Most will let you time more than one item so you can completely confuse yourself. Some have clocks built in for added stress, dinners late and not done. Finally some contain memory functions to allow you to store times and set off at specific intervals. The digital timers are, in my opinion, the best kitchen timer available.
Finally the ultimate in timing the perfect egg has to be an application I saw that runs on an Apple IPad that works just like a digital timer. That is over five hundred dollars for an egg timer. Of course it can do more than just time an egg but holy cow. Although I did not research it I am sure there are apps for your mobile telephone for these purposes as well.
From a cooks perspective I think timing food is risky at best. All times are generalizations and you should learn how to tell when the roast is medium or the cake has baked completely through. However a kitchen timer set a little before the allotted done time can allow a home maker the opportunity to go do other things around the house while a meal is cooking with an audible reminder when completion is close. Of course the kitchen timers novelty are just plain fun.