Wireless Connections and Their Reach

Hollow Oak Books uses Wi-Fi for the laptops, Bluetooth for the receipt printer, and a card reader that customers tap with their phones. Each of these is a door with no visible frame. Knowing how far each signal reaches tells you who could be standing at the door.

The rule

The farther a signal reaches, the more strangers can listen.

Common ways devices connect, from shortest reach to longest:

• NFC (near-field communication) — a few centimetres. Used for tap-to-pay and door badges. Someone must be almost touching the device.
• Infrared — needs a clear line of sight, like a TV remote. Walls stop it completely.
• Bluetooth — typically up to around ten metres, often more with good antennas. Used for printers, headsets and keyboards.
• Wi-Fi — tens of metres, through walls, out into the street and the café next door.
• Wired Ethernet — no signal in the air at all. Someone needs a cable plugged into your equipment.

Short reach is not the same as safe, but it shrinks the crowd who can try. A signal that leaves the building can be listened to by anyone nearby, so it must be protected by strong encryption and a good password.

The shortcut

Picture a circle around each device, sized by its reach. Everyone inside the circle is a possible listener. Then ask: is this signal encrypted, does it need pairing or a password, and can I shrink or close the circle when it is not needed?

The common mistake is leaving Bluetooth or Wi-Fi switched on and discoverable everywhere, all the time. When a laptop is in a busy station, turning off the radios it is not using closes doors for free.

Drills

Answer fast — trust the rule.

Remember

• The farther a signal reaches, the more strangers can listen.
• Draw a circle for each device's reach; protect, pair or switch off whatever is inside.
• Trap: radios left on and discoverable everywhere. Use WPA2 or WPA3 and a guest network for Wi-Fi.