Loud siren detector

I haven't even hooked up my system yet and already I have a suggestion.  If SimpliSafe would create a detector that could capture the shrill loud noise of another detector, it would at least allow the system to trigger an alert.  This would make it possible to integrate such things as propane gas detectors, which SimpliSafe does not yet provide.

Please, propane or natural gas detection is an obvious need.  I won't restate it here but it's really a big gap.

I am looking forward to all the things SimpliSafe does provide, of course.  Hoping within 2 weeks.

Thanks!