ISM radio band

That's John, no hotel, and craft with a kilo.

The other day, a friend of mine mentioned in passing that they'd hooked their Home Assistant dashboard to an RTL-SDR dongle to listen to the various ISM bands.

If that sounds like gibberish, let me elaborate.

Home Assistant is a tool that, among other things, allows you to control devices throughout your house.

It turns out that there are various plugins that allow you to connect it to a tool called RTL underscore 433.

More on that in a moment.

ISM, or Industrial, Scientific and Medical, is a global collection of 13 radio bands regulated by the ITU, the International Telecommunications Union, where devices are permitted to transmit all different types of signals.

Think microwave ovens, NFC or near-field communications, Wi-Fi, Bluetooth, but also weather stations, security devices, battery monitors, tyre pressure monitors, remote keyless entry, garage door openers and plenty more.

The science.

Bluetooth operates within the crowded 2.4 gigahertz ISM, industrial, scientific, and medical radio band, sharing the airways with Wi-Fi routers and microwaves.

To prevent interference, it uses frequency hopping spread spectrum, FHSS.

Rather than staying on a single frequency, paired devices acting in a local master-slave personal area network rapidly skip and hop across 79 different sub-frequencies up to 1,600 times every second in a synchronized sequence.