What Is RFID and How Does It Work? Frequencies, Range and Chip Types

A small chip on your key ring opens the front door, logs your arrival at work or unlocks a locker at the gym. It has no battery and no button, so how does it work? In a few minutes you will know what RFID is, how far a chip can be read and which chip types are in use today.

What is RFID?

RFID stands for Radio Frequency Identification. It is a technology that exchanges data wirelessly between a chip and a reader using radio waves. The chip, with a tiny antenna, sits inside a key fob, card, wristband or sticker.

Most chips you meet every day are passive. They have no power source of their own and only wake up in the reader's field. Think of it as an echo: the reader calls and the chip answers with its number. Active chips carry a battery and transmit on their own. They are used mainly in logistics and vehicle tracking.

How does an RFID chip work?

The whole exchange takes a fraction of a second and happens in four steps:

1. The reader emits a field. The antenna in the reader by the door continuously creates a weak electromagnetic field.
2. The chip powers up. When you hold the fob close, the chip's antenna draws enough energy from the field to switch on.
3. The chip answers. It sends its ID number and, with smarter types, data from its memory, which can be encrypted.
4. The system decides. The controller compares the number with its list of authorised chips and unlocks the door, records attendance or refuses access.

The door is therefore opened by the system behind the reader. The chip is the electronic key you identify yourself with.

Which frequencies does RFID use?

RFID works in three main bands, which differ in read range, speed and typical use:

Building and office access uses the first two bands. A 125 kHz fob and a 13.56 MHz reader cannot talk to each other, so always start by finding out which frequency your reader uses.

What is the read range of an RFID chip?

For access-control fobs and cards, expect a few centimetres, usually 2 to 8 cm and at most around 10 cm. The exact distance depends on the reader's power, the size of the chip's antenna and how you hold the fob to the reader.

The short range at entrances is intentional. A reader should not open the door for someone who simply walks past with keys in their pocket. Metal also shortens the range: a chip on a metal case or between coins in a wallet reads less reliably.

Other types reach further. A reader can pick up passive UHF tags on goods from several metres, and battery-powered active tags reach further still. They are unsuitable for doors, though, because the system could not tell who is actually standing at the entrance.

Which chips are used most often?

Many chip types share the same frequency and differ in memory and security. These four are the ones you will meet most often:

When choosing, think mainly about security. Chips that carry only a fixed number, such as EM4100, can be imitated, and the weak encryption of MIFARE Classic is no longer considered reliable. Where you protect a company, a warehouse or a server room, we recommend MIFARE DESFire EV3 with encrypted communication.

Our RFID key fobs come with the first three types, for example the versatile Smart model with an EM4102, MIFARE Classic 1K or DESFire EV3 chip.

What is the difference between RFID and NFC?

NFC (Near Field Communication) is a special kind of RFID at 13.56 MHz. It works over just a few centimetres, and its main advantage is that most of today's phones support it. That is how you pay with your phone, read an NFC tag or pair headphones.

Every NFC device is therefore also RFID. A phone cannot read a 125 kHz chip at all, and it often cannot reach the content of higher-frequency chips either, because that requires keys only the access system holds.

Can an RFID key fob be copied?

It depends on the chip, and this is the most important difference between the types:

• EM4100 and EM4102: yes, easily. They carry only a fixed number, which an inexpensive duplicator reads and writes onto a blank chip within seconds.
• MIFARE Classic 1K: in most cases, yes. Its Crypto1 encryption was broken in 2008 and cloning tools are widely available.
• MIFARE DESFire EV3: in practice, no. Communication is encrypted with AES-128, and without the system's keys there is nothing useful to copy.

Copying a fob to a phone works only in limited cases. An iPhone cannot emulate access fobs, and on Android it works only with some chips and readers. If copied fobs are a concern for your building or company, DESFire EV3 is the safe choice.

Where is RFID used?

You come across RFID more often than you might think:

• Building access: key fobs and cards for apartment buildings, offices and warehouses.
• Time and attendance: employees hold a chip to a terminal and the system records arrival and departure.
• Gyms and swimming pools: one chip opens the turnstile and the changing-room locker, and water-resistant fobs survive the pool.
• Payment cards and tickets: contactless payment uses the HF band.
• Identity documents: passports and many national ID cards contain a chip for contactless reading.
• Libraries and warehouses: tags speed up loans and stocktaking.
• Animals: a pet microchip works at a low frequency and holds the animal's unique number, which identifies it in a registry.

And what about RFID-blocking wallets? A metal foil shields the reader's field, so nobody can read a card through it. The risk of a contactless card being misused on the street is low, however, because banks limit PIN-free payments by amount and number.

How to choose an RFID chip for your system

Choosing is simpler than it looks. Answer three questions:

1. What does your reader support? The frequency and chip type are in the reader's documentation, or the system administrator or supplier can tell you. A matching frequency is not enough on its own. The chip type has to match as well.
2. How much security do you need? A simpler chip is enough for lockers or attendance in a small company. Companies and buildings with valuables should go for encrypted DESFire.
3. How will the chip be carried? A key fob stays on the key ring, a card fits in a wallet and can carry a printed photo, and a water-resistant fob suits the pool.

We describe the full process for building managers, companies and sports facilities, including a pre-order checklist, in our guide How to choose RFID fobs for access control and time attendance.

In our shop you will find RFID key fobs with EM4102, MIFARE Classic and DESFire EV3 chips, as well as contactless cards. Not sure which type to choose? Send us your reader model or the chip you use today and we will help.

Frequently asked questions

Does an RFID chip need a battery?
Passive chips in key fobs and cards have no power source. The reader supplies the energy, so they never run flat and last for years.

Can someone read my RFID chip from a distance?
A reader can only read a key fob or card from a few centimetres away. With encrypted chips such as DESFire, an attacker gets no usable data even up close.

Does the chip work through a wallet or bag?
Fabric, leather and plastic do not block reading. Metal and several cards at once cause problems, because the reader may not know which one to read.

Can an RFID chip be rewritten?
It depends on the type. The EM4102 has a fixed number that cannot be changed. MIFARE chips have memory that the access system writes to, for example credit or access rights.

RFID fobs for your system

Choosing the right chip is easy once you know your reader and how much protection your entrance needs. You can order our RFID key fobs individually, with optional laser engraving or full-colour printing. Write to us at sales@qscd.eu and we will find the right type together.