A facility manager in Frankfurt ordered 800 125khz proximity cards for a 12-door office building. They picked a cheap supplier on Alibaba, paid EUR 0.35 per card, and got cards that would not read on the existing HID readers. The supplier said they were “EM4100 compatible,” but they were actually a clone chip with a different modulation. Half the cards failed on the first try, and the manager had to reissue 400 cards at his own cost. Total loss: EUR 1,200 plus two weeks of employee complaints.
That story is not about 125 kHz being dead. It is about a buyer who compared price but not the chip variant, reader compatibility and modulation. A 125khz proximity card is a small product, but if it doesn’t work on your existing reader, it is useless. This guide walks through chips, compatibility, form factors and MOQ so your next order scans the first time.
What Is a 125kHz Proximity Card
A 125khz proximity card is a passive RFID card that operates at 125 kHz. It powers up from the reader’s field, sends back a unique 26-bit or 34-bit Wiegand number, and the door controller opens the lock.
Three form factors:
- CR80 thin card: 0.76 mm thick, credit card size. Used for employee badges.
- Clamshell thick card: 1.8 mm thick, more rugged. Used for parking and industrial access.
- Key fob: small plastic fob on a keyring. Used for residents and short-term visitors.
For most office deployments, the CR80 thin 125khz proximity card is the default. The pvc cards category on our site lists the CR80 sizes and material options.
Chip Variants: EM4100, TK4100 and EM4200
The chip decides whether the card is read-only or rewritable:
- EM4100: the original read-only chip. 64-bit ID, factory-programmed. Used in most new deployments.
- TK4100: a pin-compatible clone of EM4100. Cheaper, but some readers reject it.
- EM4200: read-only chip with better modulation. Used in HID-compatible readers.
- T5577: rewritable chip. Can be programmed to emulate EM4100 or HID. Used for cloner systems.
For a standard office, EM4100 is the default. If you need to clone existing cards, use a t5577 rfid card instead. The t5577 guide on our site explains how the rewritable chip works.
Reader Compatibility: Why Some Cards Don’t Work
This is where projects fail. Three compatibility issues:
- Chip modulation: EM4100 uses Manchester coding. Some HID readers expect a different modulation. A card that is “EM4100 compatible” on paper may still fail on HID.
- Wiegand format: 26-bit vs 34-bit vs HID Corporate 1000. If the card number doesn’t match the reader’s expected format, the door won’t open.
- Read range: a cheap 125khz proximity card reads 2–5 cm. A high-quality HID card reads 5–10 cm. If your reader is mounted far from the swipe point, range matters.
Before you order 1,000 cards, ask the supplier for 5 sample cards. Test them on your existing readers. The 125khz rfid reader guide on our site lists which readers pair with which chip.
Card Body: CR80, Clamshell and Key Fob
The body changes durability and use case:
- CR80 thin card: 0.76 mm, fits a standard badge holder. Used for employee IDs.
- Clamshell thick card: 1.8 mm, more rugged, survives a pocket. Used for parking and warehouse access.
- Key fob: small plastic fob, clips on a keyring. Used for residents and shared facilities.
For a new office, start with CR80 thin cards. If your employees wear them on lanyards, add a slot punch. The rfid cards for access control guide on our site lists the body options side by side.
MOQ, Encoding and Printing
Typical quote structure for a 125khz proximity card:
- Sample: 50–100 pcs, 3–5 days, usually free or EUR 20–40.
- 500 pcs: 10–15 days, EUR 0.30–0.60 per card.
- 1,000–5,000 pcs: 15–20 days, EUR 0.20–0.40 per card.
- 10,000+ pcs: 20–30 days, EUR 0.12–0.25 per card.
Encoding options:
- Factory-programmed sequential IDs: most common. Each card has a unique number.
- Customer-specified range: you tell the supplier which ID range to use.
- Variable printing: photo, barcode, and employee name on the same card.
If you are replacing an existing system, ask the supplier to match your current ID format. A 125khz proximity card with the wrong ID format is useless.
Upgrading to 13.56 MHz
If you are starting a new project, consider 13.56 MHz Mifare instead of 125 kHz:
- 13.56 MHz is more secure. 125 kHz cards are trivial to clone.
- 13.56 MHz works with NFC phones. Employees can use their phone instead of a card.
- 13.56 MHz readers are widely supported by access control software.
For a new build, spec 13.56 MHz. For a retrofit on existing 125 kHz readers, stick with a 125khz proximity card until you can budget a full reader replacement.
FAQ
What is the difference between a 125khz proximity card and a 13.56 MHz card? 125 kHz is read-only, cheap and easy to clone. 13.56 MHz is rewritable, secure and works with NFC phones.
Can I use a 125khz proximity card on an HID reader? Sometimes. HID readers expect HID-proprietary modulation. Ask for samples before you order.
How many cards can I order for a pilot? Most suppliers start at 500 pcs. We do 100 pcs for trial runs.
Can I print my own logo on the card? Yes. Full-color CMYK on both sides is standard on any 125khz proximity card order.
If you are rolling out a new office or replacing an existing system, send us your reader model, ID format and quantity. We will quote the card with a sample stage and a batch test report, usually within one working day.