How can I time myself when I run?

I have been reading in the Internet about training for a 5k. In the mayoclinic website , they said that I need to run for 15 seconds and then walk for 45 mins.. Well what kind of device do you you use to time your self? I need like something that peeps that can tell me when does the 15 seconds end and when should I start walking etc etc

Help.. :(

I don't want to use a watch. Or the phone

What do you use?