Safety and Security

It is dark. You hear a beep.

It is dark. Another beep.

You check the time. It’s almost 2.30am.

Another beep.

What is that?

Is it from outside?

You open a window and wait.

You hear a beep.

It’s not outside. That must mean it’s inside. That means it’s your problem.


There are lots of things it could be. They’re all over the house. From the fridge to the carbon monoxide detectors.

Bleary eyed you stalk around the house, stopping occasionally to see if you can hear the direction of the beep.

Going in to one room, doubling back on yourself.

Eventually. A beep above your head. A smoke alarm. Of course it is.

Your child is asleep in the next room. He doesn’t sleep well. You have to silence the smoke alarm quickly and quietly.

What does the beeping mean? The house is not on fire. You happened to have gone around the house already.

The beeping could mean anything. You don’t know the cause. Your mind races. The smoke alarm is mains powered. The smoke alarm could have lost power. Did you do anything recently that might have caused the smoke alarm to have lost power? Has there been a power cut? Could the battery have lost power? Does it have a battery? Should the battery have lost power if it’s been running off mains? How would the smoke alarm know the battery is dying if it mains powered, it isn’t using it.

You check online for anything else it could be. It’s 3 am. You want to sleep, not diagnose a beeping smoke alarm that will wake up your family.

There are loads of websites giving you lots of options depending on the type of smoke alarm you have and the kind of beep it’s making. You don’t know the make and model of my smoke alarm, they came with the house.

Apparently it’s common for batteries to start failing during the night when the tempurature drops, causing the battery to be less effective.

All the smoke alarms are on their own circuit. You could turn the whole thing off and worry about it in the morning. It seems unlikely there would happen to be a fire just then. But would that make things worse? Would the smoke alarm keep working off their batteries and drain them faster causing more of them to beep? Would it set all the smoke alarms off as a failsafe?

Your best bet is to replace the battery. Often people don’t know that a beeping smoke alarm means the battery needs replacing.

Is there a spare? Yes. Fortunately. Lets not think about what you would do if that wasn’t the case.

It’s also fortunate this is not one that needs a massive ladder to reach.

Now how do you replace the battery? How do you open the smoke alarm?

Written on the smoke alarm is an obscure instruction about pushing a screwdriver in to a hole on the side. Looks like you’ll need to find a screwdriver then. Why do you need to find a screwdriver at 3.30am? Fortunately you know where one is.

You follow the instructions. The smoke alarm is slightly too close to the wall and the screwdriver almost doesn’t fit. You still cannot work out how to get the old battery out. Your arms are so tired from holding them above my head for so long.

You’re frustrated, angry. You lose it. You pull on the case. Maybe there is a way in. After easing it a bit, it comes away.

No access to the battery.


At least now you can see how you would get to the draw that holds the battery.

After a bit of prying a draw pops out and the battery drops out of the draw.

Replace the battery. Put the draw back in.

No beeping?

Go back to bed.

The adrenaline is surging.

You’re waiting for the next beep. Was that a beep?

You stay awake until your son wakes at 6.30am.

The next morning#

Your electrician advises that there are very high voltages in the smoke alarm due to the electronics used to check for smoke. Removing the case was dangerous. It is best to replace the unit.

Given no one knows the age or history of any of the smoke alarms and that you have a young family you make the decision to replace them all.

The electrician recommends the most popular brand. It’s the exact same model you already have.

At least you know how to replace the battery now.


For the UK the regulations used to say that, when adding a loft extension to your house, that all doors were replaced with firedoors that self close.

People found all the doors in your house being closed was inconvenient, this lead to people propping the doors open. So the regulations were changed to install smoke alarms in all rooms that are linked.

This is incredibly sensible and pragmatic advice that responds to people’s real-world usage of safety equipment.

When talking about security I regularly like to frame it to the world of safety. Safety is tangible and people like talking about safety. But I recognise that they’re often not directly comparable.

Safety equipment is often tied to a regulations that can be complex and expensive to change. But safety equipment can also have the same failings as a lot of security products do. Poor documentation. Poor user experience, especially when things go really wrong. Poor quality alerts.

If you want to build good, reliable, and accurate equipment you need to think about how they fail, and how your users will over-come the failure.

Because right now I don’t want smoke alarms in my house. I would rather have a relaxing and peaceful night sleep. I won’t be alone in that motiviation.

I wish this story was not based on real events.