nootropic design now sells relay modules and sirens to make it your Defusable Clock much louder and to make it easy to connect other external devices (e.g. a smoke grenade or servo motor).
I don’t know anything about smoke grenades and have never used one.
The relay can switch a very large amount of current (5A at 24VDC), so I suspect it can handle the current to 2 devices. The siren will not represent that much current.