How an RFID time clock works
An RFID time clock reads a small chip in a card or key fob. Each chip has its own number. Choosing an RFID card reader for a time clock comes down to two things: the frequency and how the reader talks to the tablet. The worker taps the card on the reader, the reader sends that number to the time clock, and the time clock records a punch for the person the number belongs to.
Nobody types anything, so it is fast at the start of a shift. It also works with gloves on, which a touch screen does not. That is why many warehouses, workshops and building sites prefer an RFID card time clock, sometimes called an RFID employee time clock, to a PIN pad.
With a tablet time clock you do not need a special wall terminal. A cheap USB reader plugged into the tablet does the job.
125 kHz vs 13.56 MHz: which frequency to choose
The first choice is 125 kHz vs 13.56 MHz. Readers and cards must use the same frequency. A 125 kHz reader cannot read a 13.56 MHz card, and the other way around, unless you buy a dual-frequency reader.
| 125 kHz (low frequency) | 13.56 MHz (high frequency) | |
|---|---|---|
| Common chip names | EM4100, TK4100; also HID Prox style cards | MIFARE Classic 1K, other ISO 14443A cards, NFC tags |
| What the reader gets | A fixed ID number | A unique ID number, plus memory the time clock does not need |
| Price of cards and fobs | Usually the cheapest | Usually a bit more |
| Read by a phone with NFC | No | Usually yes |
| Good for a time clock | Yes, simple and cheap | Yes, and handy if you already use these cards |
125 kHz prox vs 13.56 MHz: the short answer
If you are starting from zero, 125 kHz EM4100 cards and fobs are the simplest and cheapest choice. If your building already uses access cards, check which frequency they are. Workers then carry one card for the door and the clock. Ask the access control installer, or test a card on a dual-frequency reader.
HID Prox and similar branded proximity cards are 125 kHz but use their own formats. Many cheap readers only read EM4100 style cards. If you need to read existing branded cards, check the reader listing names those cards before you buy.
USB RFID reader with keyboard emulation
A USB RFID reader with keyboard emulation looks like a keyboard to the tablet. When you tap a card, it types the card number and presses Enter. That is why it needs no driver and no app. It works on Android tablets, iPads with the right connector, Windows, Mac and Linux.
- Plug the reader into the tablet. Use a USB-C to USB-A adapter (often sold as an OTG adapter) if the tablet only has USB-C.
- Open any notes app and tap a card on the reader.
- A row of digits should appear, followed by a new line. If it does, the reader works as a keyboard.
- Open the time clock and enroll each card by tapping it while the worker profile is open.
iPads with a USB-C port accept a USB keyboard, so they accept these readers too. Older iPads with a Lightning port need Apple's Lightning to USB Camera Adapter. Some Android tablets only charge or only use USB through one port, so pick an adapter with a charging pass-through if you want the tablet to charge at the same time.
Why the number on the card does not match
Readers can output the same chip in different formats, such as 10 decimal digits or 8 hex characters. The number printed on the card may use yet another format. This does not matter as long as you enroll and punch with the same reader, or with readers set to the same format.
RFID cards vs key fobs
An RFID key fob and a card hold the same kind of chip. The difference is how workers carry them.
- Key fobs live on the key ring, so people rarely forget them. They survive pockets, dust and rain well. You cannot print a name or photo on them.
- Cards are CR80 size, like a bank card. You can print the worker's name, photo and company logo, and wear them in a badge holder on a lanyard.
- Cards with a slot punched in them clip to a badge reel without a holder.
- Wristbands and stickers exist too, but fobs and cards cover most small teams.
A common setup is an RFID key fob 125 kHz for each worker plus a few spare cards for visitors and new hires. If workers already wear a photo badge, use cards so the badge and the punch card are the same thing. For badges without a chip, printed QR codes are the other option.
What to buy and what it costs
These are typical price ranges we saw on large online marketplaces in early October 2026, before tax and shipping. Prices change often and vary by country, so treat them as a rough guide.
| Item | Typical price range | Notes |
|---|---|---|
| USB RFID reader 125 kHz | About $10 to $15 | Plug and play, EM4100 cards only |
| Dual-frequency USB reader (125 kHz and 13.56 MHz) | About $20 to $35 | Reads both families; check the listed chip types |
| Brand-name enterprise reader | Often $150 or more | Reads many card formats, configurable output |
| 125 kHz key fobs, pack of 100 | About $15 to $25 | Read-only EM4100 or TK4100 |
| 125 kHz CR80 cards, pack of 100 | About $15 to $30 | Plain white, some printable |
- USB reader 125 kHz: about $12
- Key fobs, pack of 100: about $20
- USB-C adapter: about $5
- Total: about $37 one time
- Spare fobs left: 88
That one-time cost is the hardware side of an RFID time clock with no subscription for the reader itself. The software is a separate choice. ClockBadge Time Clock will be free for up to 3 employees and €3 per employee per month after that.
USB RFID reader not working? Quick fixes
If a USB RFID reader is not working, run the notes app test first. It tells you whether the problem is the reader or the time clock.
- No light or beep: the tablet is not powering the reader. Try another adapter, or one with power pass-through.
- Light but no digits: the card is the wrong frequency. A 125 kHz reader stays silent with a 13.56 MHz card.
- Digits appear in notes but not in the time clock: the time clock screen did not have focus. Tap the punch screen once, or check its badge setting.
- Different digits each time: two cards are touching the reader. Keep one card per tap.
- The on-screen keyboard disappears on Android: that is normal while a hardware keyboard is connected.
Security: copying cards and buddy punching
Simple 125 kHz cards are easy to copy. Fob copiers are sold openly. For a door lock that is a real concern; for a time clock, the bigger risk is plainer: one worker taps a colleague's fob. That is called buddy punching.
An optional photo at each punch is the easiest fix. The manager can check the photo when a time looks odd, and most people stop sharing fobs once they know it is there.
Questions
What is the difference between 125 kHz and 13.56 MHz RFID?
They are two radio frequencies, and cards and readers must match. 125 kHz cards such as EM4100 are simple and cheap and carry a fixed ID. 13.56 MHz cards such as MIFARE Classic can also store data and can often be read by phones with NFC.
Can a phone read 125 kHz RFID?
No, a phone cannot read 125 kHz RFID. Phone NFC works at 13.56 MHz only. To read 125 kHz cards or fobs you need a separate 125 kHz reader, for example a small USB reader plugged into the tablet.
Do USB RFID readers work with an iPad?
Yes, a keyboard emulation USB RFID reader works with iPads that accept a USB keyboard. iPads with USB-C need at most a USB-C to USB-A adapter. Older Lightning iPads need Apple's Lightning to USB Camera Adapter.
What does keyboard emulation mean on an RFID reader?
Keyboard emulation means the reader acts like a USB keyboard. When you tap a card, it types the card number and presses Enter. No driver or app is needed, so it works in a browser-based time clock on most tablets and computers.
Is a key fob or a card better for a time clock?
A key fob is better if workers do not wear badges, because it lives on the key ring and is hard to forget. A card is better if you want a printed name and photo on a lanyard. Both hold the same kind of chip.
How much does an RFID time clock setup cost?
The hardware is cheap. In October 2026 a basic USB 125 kHz reader cost about $10 to $15 and 100 key fobs about $15 to $25 on large marketplaces. Software is separate; ClockBadge will be free for up to 3 employees.