The Panic Button in MIDI Designer sends a Note Off for all channels and notes. [ User Reference Guide on Panic Button ]
Note, however, that you can also use MIDI messages for a Panic Button. Depending on your MIDI target, this might work better: fewer MIDI messages sent and the MIDI target can optimize its response.

On the other hand, your MIDI target could also ignore these messages or just use them as regular control change messages.