How do you use a double tap to turn on a different module?

[kenny]

I have read that you can use a 2 way switch
to control both the local unit as well as a
secondary unit.  Does anyone know how to do
this?  I tried setting up a macro with a
condition that the first unit be on before
the second unit would turn on but it didn't
work.  It executed every time and turned on both.

Any ideas?

Thanks.