the signal device is free to fall by {TAIL ~ gravity} into {HEAD ~ a vertical position} when triggered by opening the mailbox door 
the signal device is free to fall by { TAIL ~ gravity } into { HEAD ~ a vertical position } when triggered by opening the mailbox door
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH