Docedison:
And to use a transistor to control the relay. NEVER connect a coil Like a RELAY COIL TO AN Arduino pin, unbuffered.Bob
Well that is a little drastic isn't it? There are many small DC 5 volt reed relays that draw well less then 30ma and as long as you install a diode across the relay coil terminals you can drive them fine directly from a arduino output pin, I've done it frequently with no drama. 
Lefty