Optonic owned the patent hence why no one else produced alarms until the patent had run out from memory around 1992 , the flood gates then opened hence the amount of alarms on the market . As soon as the patent run out the big boys of the time i.e Shakespeare , Daiwa , Fox all started to produce roller alarms .
Another tip is to eliminate draughts.... wear a scarf or shemagh, tuck your joggers into your socks or get a pair of boot gaiters... don't wear trainers.... get a good pair of boots, preferably thermal types that you can get in and out of quickly... after lugging your gear to your swim/pitch & setting up you'll be sweating cobs... take off your boots and put on a fresh pair of dry socks... and some dry clothes... it don't half make a difference...!
The thing is the system Delkims use only exists due to the patents at the time , they couldn't use a roller so had to come up with another solution a good one maybe to sensitive probably .Alot of takes are more than one bleep so most alarms will suffice . If you want to see all the action use a float lol .