You can start or stop the countdown simply by rotating the timer. There are three volume levels (high, low, silent) as well as a flashing LED light for visual alert so if you work in a quiet office, you won't disturb your co-workers!
Promising review: "No joke, this timer is COOL! I never thought I’d be saying that about a timer, but it’s the truth. I bought the timer to help me focus at work. I tend to lose track of time and lose a lot of it. With this timer, all I do is flip it over to whatever time I want countdown. When time is up, it will beep to let me know and then even count up to show me how far past I went. It’s very stylish and cool looking, and all my coworkers asked me about it. I highly recommend this timer for anyone who needs needs help focusing and who loses track of time." —Julia
Get it from Amazon for $16.99 (available in four colors).