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