I can remember at Alderney that was the case indeed you could sit outside on a bench in the sun until called for boarding. That was about 10 years ago, not sure if it's still like that but I suspect so.
Current picture at Alderney:
There are no x-ray scanners although there are hand held metal detectors. So when you arrive your hold luggage is weighed on "I speak your weight" type scales.
It is then manually searched in your presence and when cleared, taken through to be put on a cart airside
You then wait in the terminal landside, go through a slimline upright metal detector when called, and your minimal (laptop/handbag sized) hand luggage is searched.
Once airside, you are required to go into a portacabin where you watch the flight safety video, after which you remain there or can sit on the bench outside the cabin. You're still in a compound down some steps from the apron, so not exposed. When the flight is ready you walk to the plane (if you have a pet then you also take your dog or cat to the back of the plane yourself and it is loaded into the hold).
Once you arrive into Southampton or Guernsey, there is no direct transfer to the next flight - you have to clear arrivals and reclaim and then recheck your bag into the standard security pathway, to effectively enter the UK and international screened baggage system at that point. The manual checks at Alderney are only valid till you reach the first airport with standard scanners, in other words. This also seems to apply to pilots and crew who I have often seen scanned with metal detectors when they deplane at Guernsey on arrival from Alderney. This seems to mirror the discussion above about HIAL.
As an aside, there is no door or bulkhead into the cockpit on the Aurigny Dornier 228s so you can see the flight deck and pilots throughout. There is now a bulkhead between cargo/hold and the passenger cabin, compared to the BN Trislanders which often had the cargo just contained in cabin but held back by a net, so bags could in theory be accessed.
I first travelled through Alderney in the second half of September 2001 so witnessed first hand the improvised belt and braces security measures that had been introduced a week earlier. Very little has change since, mainly due to the constraints of the terminal. Alderney is likely to acquire a new airport in the next few years. This will mean a transition from the Dornier 228s (19 seats) to ATRs. Alderney's little airport will be missed by many, it's very much like being in a 1950s built primary school prefab.
As an aside, being so small a lot of Ridunians have second jobs, at one stage the chap that searched your bags at the airport also worked as the undertaker.
Most airfields you're lucky that there's a hut with a cup of tea! Bonus if there's someone around to do the radio.
-make that dream a reality.