Wireless and Short-Range Communication

Four technologies, one axis worth memorising: range

Questions on this topic almost always ask "how many of the following are short-range" or ask you to match a technology to its typical use. Both formats collapse to the same underlying fact: these four technologies are separated primarily by range, and everything about how each is used follows from where it sits on that scale.

NFC: deliberately too short-range to be a problem

Near Field Communication (NFC) is deliberately built with an extremely short range, a matter of centimetres, and that limitation is the entire security feature. A contactless payment card or a phone tap-to-pay system relies on NFC precisely because an attacker would have to be within touching distance to intercept anything, which is a much harder attack to pull off unnoticed than intercepting a Wi-Fi signal from across a room. NFC also supports genuine two-way communication, unlike the smart cards that preceded it, which is why it can both read and write data during a single tap.

RFID: identification, not payment

Radio Frequency Identification (RFID) exists to identify and track objects rather than to move meaningful data between two active devices, and it comes in two forms that behave very differently.

Passive RFID tags carry no power source of their own. They draw their power from the reader's own signal, which is why their range is limited to a few metres, and it is also why they can be made extremely cheap and small, printed onto a label rather than built as a device. This is the form used for retail inventory tags and toll-collection stickers.

Active RFID tags carry their own battery, which extends their range dramatically, up to 100 or even 200 metres, at the cost of size, expense, and a finite battery life. This is the form used for tracking high-value shipping containers or vehicles over a wider area.

Bluetooth and Wi-Fi: personal area versus local area

Bluetooth and Wi-Fi occupy similar physical ranges, up to roughly 100 metres, but are built for different jobs. Bluetooth is designed as a Personal Area Network technology: connecting a small number of nearby personal devices directly to each other, a phone to headphones, a laptop to a mouse, with low power consumption as the priority. Wi-Fi is a Local Area Network technology: connecting many devices to a shared network, typically through a router, at much higher data rates, with power efficiency a secondary concern.

Quick revision points

• NFC: ~10 cm range, 13.56 MHz, deliberately too short-range for most eavesdropping to be practical, supports two-way communication (read and write) in a single tap. Used for contactless payment.
• RFID: identifies and tracks objects rather than transferring data between active devices. Passive tags have no power source, draw power from the reader, range a few metres, cheap (retail tags, toll stickers). Active tags carry their own battery, range up to 100-200 m, used for tracking high-value assets over distance.
• Bluetooth: Personal Area Network, connects a small number of nearby personal devices, prioritises low power.
• Wi-Fi: Local Area Network, connects many devices through a shared router, prioritises data rate over power.
• The single fact that answers most questions on this topic: range, from NFC's centimetres to Bluetooth and Wi-Fi's roughly 100 metres, with RFID spanning both ends depending on whether it is passive or active.