You don’t have to be a nuclear physicist to realize that whatever microwave ovens do to food should not be done to humans. In fact, they work by passing microwave radiation through the objects placed inside them, causing water molecules in these items to rapidly heat up.

It’s therefore pretty important that this radiation doesn’t escape the microwave and start zapping people standing nearby. Given that kitchen appliances have to pass rigorous safety tests before they can go to market, most of us trust them not to leak.

However, as this eye-opening video from YouTube channel Physics Girl reveals, there is a way to check how effective your microwave is at keeping this radiation contained, and the results might surprise you.

Like microwaves, cell phones emit radiation, albeit at a different frequency. Therefore, by placing your phone inside your microwave and closing the door, you shouldn’t be able to call it, as the waves shouldn’t penetrate the door.

However, as the video shows, you might just find that your phone rings even when it is inside the microwave (which, by the way, should absolutely not be turned on at this stage!). If this happens, it could mean that your appliance is leaky, or it could just mean that your particular model is designed only to contain radiation at certain frequencies; microwaves typically have a frequency of 2.45 gigahertz, while cellular waves are usually either 1.9 gigahertz or 850 megahertz.

Fortunately, even if your microwave is leaky, it’s unlikely that the escaping radiation will actually do you any harm.