That opened the way for others, and when he was offered one he didn't hesitate, although he didn't believe his business was especially vulnerable.
Read more: Kaitaia police warn robbers - you will be pinged
Knifepoint robbery of Northland tavern - cash taken, owners tied up with electrical cords
Northland dairy owner threatens hunger strike over youth offending
Knife-wielding robbers demand Whangarei dairy owners hand over baby
His staff were grateful all the same.
They're looking after us," said Leanne Kelly, who has been there for two years.
The drill was that at the first sign of trouble the fog machine would be activated, any staff in the shop then changing their position before heading for the back room.
It all went according to plan when Mr Allan demonstrated the machine on Friday, although the extremely piercing alarm took some turning off.
He was last seen flapping a clipboard to help restore everyone's 20/20 vision.
And if the fog, which is odourless and harmless, didn't deter would-be robbers, Mr Allan said, the cameras that he had mounted outside the service station should.
They provided a well-defined record of everything that moved, out to and including the highway, in both directions, an investment that he described as a public service.