I arrive home from the supermarket, unnerved and empty-handed.

“How did it go?” my wife asks.

“I set off the alarm twice,” I say. “It took me 15 minutes to get it started.”

“That happened to me yesterday,” she says.

“Now I can’t open the back to get the food out,” I say. “I give up.”

Everything about our new car is great, apart from its capricious security system. The vehicle was delivered by its previous owner – my father-in-law – with a single instruction for making it go: depress the button on the key as you turn it in the ignition. But this doesn’t always work. Sometimes nothing happens. Sometimes the alarm goes off. Sometimes the car locks you in. Sometimes it refuses to let you have your shopping.

“That’s also happened to me,” my wife says. “You need to push the button twice, start the car, turn it off and then manually unlock all the doors from the inside.”

“I tried that,” I say. “I tried everything.”

“We need to sort this out,” she says. “It’s getting worse.”

“How can it be getting worse?”

“I don’t know,” she says. “The manual doesn’t say anything about the alarm.”

I go online to investigate, but the car, though new to us, is 13 years old – most web forums devoted to dysfunctional car alarms address modern problems. Discussions about older models are tinged with despair: people post various theories (“Sounds like your car is operating in passive arming mode”), none of which proves helpful to the original petitioner, who eventually disappears. I imagine a car like ours in flames at the bottom of a canyon, alarm still blaring.

“Have you sorted out the car yet?” my wife asks the next day.

“No,” I say. “Yesterday it let me start it first time.”

“Me too,” she says.

“But then this morning the alarm went off when I wasn’t even in the car. I was just walking by it, on my way to the shops.”

“You must have done something it didn’t like,” she says.

“I’m supposed to drive to Swindon on Friday,” I say. “I can’t have this shit happening to me there!”

That night I am woken at 4am by the sound of a car alarm. When I pull back the curtains I see our car across the road, gleaming in the light of a street lamp. My wife joins me at the window.

“Why is it doing that?” I say. “There’s no one near it.”

“Did you accidentally press your key?” my wife asks.

“I don’t sleep with my keys,” I say. “Why aren’t the lights flashing?”

“Because it’s not our car alarm,” my wife says. “It’s another car, down the road.”

“What?” I say. “How can it do that?”

“Don’t be stupid,” she says. “Go back to bed.”

On Saturday, the day after getting locked out of the car on a rainy night in Swindon, I remove the leather binder containing the manual from the glove box. Beneath it I find something poking out of a hidden flap: a slim, ancient volume entitled Category 1 Alarm System Operating Instructions.

“A whole book about the alarm?” my wife says when she sees it on the kitchen table.

“Yes,” I say. “And I am the first person ever to have read it.”

“What does it say?”

“It says many things, but the answer to our problem is on page four: press button to disarm.”

“That’s it?”

“You then have 30 seconds to start the car. If you miss your window, repeat step 1.”

“It can’t be that simple,” she says.

“I’ve tried it, and it is.”

“So my dad’s method was bollocks.”

“I couldn’t possibly comment,” I say.