A reader said she saw me in her city. “But I’ve never been there,” I said. “I just have a common face.”

This happens a lot. I once recognised myself on the other side of a crowded bar once before, realising that it was probably someone else. (It was late and drink was involved.)

Anyway, having a common face was never a worry until this week when automated face recognition devices started springing up everywhere.

At Hong Kong airport outbound immigration desk officers are being replaced by cameras and Delhi railway station will soon have face recognition devices on platforms.

Russians are developing a device that recognises faces and tells the user their names. Whenever it hears you say: “Of course I remember you, you’re, um…” it will instantly search the database and whisper an answer in your ear, which you can then use to impress the person with: “You’re… Mr… Notfoundin Database.”

News articles mention that there could be problems, but the writers don’t realise there already are. In Shenzhen and other Chinese cities, secret cameras photograph your face if you cross the road before the green man is flashing, and put your name, age and address on a giant “wall of shame” screen. This enables outraged citizens to give you suitable punishment, such as burning down your apartment block and cursing your family for seven generations.

Three Chinese women who went to South Korea for beautifying plastic surgery earlier this month got stuck at the outward immigration desks since they no longer looked like the photographs in their passports. Try explaining to a camera: “But surely you don’t prefer my previous nose?”

Now face recognition is coming to our phones. If you’re kidnapped and your abductors give you a black eye, your phone will lock itself and say: “You’re not my master, you lumpy-faced stranger.”

Japanese scientist Shigeomi Koshimizu got over the facial changes problem by inserting 360 hidden sensors into a seat to precisely measure your bottom. He put the device in a car and programmed the vehicle to turn itself on if it felt that your butt was familiar. Some scientists say butt-triggered security devices are the way of the future.

This seems risky, given the rising obesity rates. “Hello, boss? I can’t come to work today as my car thinks my bottom is too fat.”

One reader, businessman Karuna Menon, said he liked the idea. He said that the next time a guy’s wife asks if her butt looks big, the husband can just say: “I dunno, ask the car.”

What about those of us with common faces? A techie friend said that Apple had calculated that the odds of someone having a face similar enough to be able to unlock your phone is literally one in a million. That means there are 7,499 people in the world with a face exactly like mine. Poor them.

I shared this factoid with my kids and they were typically pragmatic about it. “If you die, Daddy, we can just get another one.”