All you need is the Internet. There is a free online metronome available at metronomeonline.com
It’s easy to use – just click on the tempo you want. Click ‘off’ when you want it to stop, and it will even give you a concert pitch ‘A’. Best of all, it’s free!
I have referred a few of my students to it now who otherwise wouldn’t have access to a metronome except during lesson time. Sometimes the Internet is handy ;D