About a year ago, I started to hear of strange goings-on with Macs, more specifically MacBook Air and MacBook Pro models with M1 chips. Several users complained that, when put to sleep overnight, they woke themselves up, and by the morning their batteries had discharged significantly. At the time, I noticed something odd myself. Sometimes, when I put my iPad Pro on top of the case of my M1 MacBook Pro, the computer started up spontaneously.

Although fewer users continued to complain of their Macs not staying asleep, every now and then, my MacBook Pro continued to start up despite it being left shut, and shut down. Recently I’ve been using my iPad Pro a lot, and this problem came to irritate. At first I thought it only occurred when the iPad was charging, but then I discovered that it wasn’t the iPad that was responsible: it was down to magnetism.

Others had noticed the same phenomenon a year ago, and realised that what was happening was that a magnet was coming close, or in contact with, the left side of the upper case of the MacBook Pro or Air, and triggering the sensor it relies on to tell when the case is opened. Unlike some previous models, these M1s can’t have this automatic startup disabled, and many are also set so that they don’t sound the startup chime either.

My iPad Pro has a minimalist case, whose top cover hinges with a long, thin magnet, which retains it against the side of the iPad. I’ve been able to reproduce this startup behaviour using just that cover with its magnet and without the iPad.

As this is detected by the MacBook Pro or Air as if the lid is being raised, if it’s asleep at the time that the magnetic field triggers the sensor, it wakes up; if it has been shut down instead, it begins the startup process. My MacBook Pro’s startup chime is enabled, but if it wasn’t, I wouldn’t be aware that it had started up at all, at least not until I came to use it next.

In the distant past, experience taught me to keep magnets and computers well separated. One quick wave of a small magnet was often sufficient to destroy the data stored on a floppy disk, and placing a magnet near a CRT display resulted in unpleasant image distortion. Over the years since, I’ve remained wary of magnets getting too close to computers, although risks have declined, at least until now. I’ve got magnets on iPad covers, built into little gadgets to let them stick to ferrous surfaces, even in the strap of my Apple Watch. Little did I realise how they could come to control my Macs.

So if your MacBook Pro or Air ever wakes or starts up unexpectedly, look first for magnets. If you’ve got sleeves or covers which incorporate magnets to stick keyboards to, keep them well away. And whatever you do, be careful what you put on the left side of a closed MacBook Pro or Air.

I wonder whether my new MacBook Pro M1 Pro will be prone to the same mysterious behaviour.