The current flow produces {HEAD ~ a potential difference} across {TAIL ~ the first diode} to turn on another transistor to cause an alarm to be given 
The current flow produces { HEAD ~ a potential difference } across { TAIL ~ the first diode } to turn on another transistor to cause an alarm to be given
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH