Nothing.
The best selling car of its time - the 1980's and 1990's. The 2.0 Ghia and 2.0 Ghia injection were the class acts of the range. The first run for three years was a silver 5dr model, an automatic with a radio cassette, electric aerial, and a glass sunroof, it covered 15k miles with no problems. The 100 hp engine providing good performance.
Replaced by the 2.0i Ghia in metallic blue. This version had one of the first on board computers and a quartz clock. The computer could not do much. It told you what doors were open. A slightly better performer than the 2.0 no I Ghia. It could top 115mph, and do 25mpg or so, as it was an automatic. Add 20% for the manual version.
The strange delayed reaction auto box always kept performance leisurely. It oozed Ford class and was actually little different to drive, if not slightly nicer than the Granada 2.8i Ghia run at the same time. The two had a similar corporate look and feel to them. The Sierra gave good service up hill and down dale, to the shop and back, never breaking down or missing a beat, until one day it was rammed up the back by a boy racer. A new body shell was needed!
This fitted, the car continued to give service. Now given to my sister to drive as her own car. It began to get grubby as horse riding gear was put into it, and was not cleaned much.
Then one day it was gone. Stolen in the night from a country road outside a farm house. Is it safe nowhere for an old car nowadays? It seems not.. Some joy riders had driven down from the North, stolen it, and dumped it with all the doors and windows open after reving the engine till it blew up. In the middle of a wood and too old for any repairs, so it was off to the crusher, even though it was only 10 years old. What a way to go!
The door open telltales were not computer controlled. They're just operated by switches in the doors - nothing particularly clever.