Burlar alarm output conversion?

[Martin Howell <martin.howell@xxxxxxxxxxxx>]

I want to interface a cheap burglar alarm into my central indicator
panel, so that I can see if its been triggered while I've been out.
Also, I'd like to hook it up to an internal siren to scare the poop out
of the burgling person  The alarm has a built-in oscillator to drive its
internal siren, and I'd like to find a way to convert this into a
latched output that will keep a LED on long after the siren has run out
of puff.  There must be a simple logic device that will do this, but I
ain't clever enough to know what it is - anyone able to help, pretty
please?

Martin