Why does frequency decide everything?
Frequency is the most important fact about an access credential, because a reader can only energize and talk to a tag tuned to its own band. A 125 kHz reader broadcasts a low-frequency field a 13.56 MHz chip cannot answer, and vice versa. The two bands use different antenna geometry, modulation, and chip families, so they are not interchangeable. That makes frequency the fork in the road for ordering a compatible card: specify a 13.56 MHz blank for a 125 kHz door and it is inert no matter how the data is encoded. Identify the band first, then narrow down the format within it.
How do I tell which frequency I have?
Most cards do not print their frequency, so you read the clues. The fastest reliable signal is the printed part number or the reader model: look those up and the band is usually documented. A quick behavioural check narrows it further before you order a replacement.
- Printed markings: EM4100, T5577, HID 1326 ProxCard II, or Indala points to 125 kHz LF; MIFARE, DESFire, iCLASS, Seos, or NTAG points to 13.56 MHz HF.
- Reader model: identify the reader and check its rated frequency; the card must match it.
- Phone NFC test: if an NFC app detects a UID or chip type when you tap the card, it is HF. Silence usually means LF (or a secured HF chip the phone cannot read).
- Behaviour: LF prox reads at a short tap distance; HF smart cards often involve a brief handshake.
What lives on 125 kHz (low frequency)?
The 125 kHz band is the home of classic proximity. The dominant read-only chips are the EM4100/EM4102 family (and the larger EM4200), which emit a fixed ID and nothing more, while programmable blanks like the T5577/ATA5577 and EM4305 can be encoded to present many formats. That is what makes open LF credentials straightforward to supply on a compatible blank.
On top of those chips sit the familiar proximity formats: HID Prox (ProxCard II, ISOProx, the open 26-bit H10301 and friends), Indala, and AWID. Because most are open, non-proprietary industry standards, a compatible blank can be encoded to carry the same facility code and card number and read identically at the door.
What lives on 13.56 MHz (high frequency)?
The 13.56 MHz band carries true smart cards built on ISO/IEC 14443 (genuine NXP MIFARE Classic, MIFARE Plus, Ultralight, DESFire EV1/EV2/EV3) and ISO/IEC 15693 (iCODE), plus NFC Forum tags like the NTAG21x series. These chips have memory and, in the secured tiers, onboard cryptography. HID's HF line lives here too: legacy iCLASS (Picopass), iCLASS SE, and Seos, the highest tier.
The honest distinction is the credential's security tier. Open or legacy HF data can usually be encoded onto a compatible blank, while secured smart credentials — DESFire with AES, MIFARE Plus in secured mode, iCLASS SE/Elite, and Seos — are protected by design. For those we supply compatible blank credentials on the matching chip platform; your own system or integrator enrols them with its keys, exactly as it would credentials ordered through the OEM channel. The keys, and your site security, stay in your hands.
What about dual-frequency cards?
Some credentials carry two chips in one body: a 125 kHz LF antenna and chip plus a separate 13.56 MHz HF antenna and chip. These dual-technology or migration cards let a site run old LF readers and new HF readers side by side during a rollout, and a single card opens both.
If you are mid-migration, identify which band each door uses. A dual-frequency compatible card must match the LF format on the legacy doors and the HF chip platform on the upgraded ones. When you request a quote, give us both bands and the exact formats so the blank satisfies every reader the card touches.
Why must the frequency match for a compatible card to work?
A compatible card is only useful if the reader can talk to it, and that conversation starts with the radio band. Match the frequency first, then the chip family, then the exact format and bit length. Get the band wrong and nothing downstream matters; get it right and we can usually supply a compatible blank as a cost-effective alternative to OEM credentials.
If you are unsure, send us the card's printed markings and reader model, or a phone NFC test result. That is enough for us to confirm the band, identify the format, and advise whether we can encode it directly onto an open blank or supply a compatible blank your system enrols. We are an independent manufacturer and supplier, not affiliated with any of these brands.
125 kHz LF vs. 13.56 MHz HF at a glance
| Trait | 125 kHz LF | 13.56 MHz HF |
|---|---|---|
| Common chips | EM4100/EM4200, T5577, EM4305 | Genuine NXP MIFARE Classic/Plus, DESFire, iCLASS/Seos, NTAG |
| Typical formats | HID Prox, Indala, AWID, EM | MIFARE/DESFire app data, iCLASS, Seos |
| Security | Open, non-proprietary standards | Ranges from open to strong AES/3DES crypto |
| Phone NFC reads it? | Usually no | Usually yes (UID at minimum) |
| How we supply it | Open formats encoded directly to a compatible blank | Open/legacy encoded directly; secured tiers supplied as compatible blanks your system enrols |