Will an NFC card open my gate? The answer is a frequency, not a brand
A card that shares your number and a fob that opens the gate are two different pieces of radio. Sometimes they can be the same piece of plastic. Here is how to find out before you order anything.
If you run a marina, a yard or a caravan park, you have almost certainly been asked some version of this: can we not just have one card that opens the gate and has our number on it? It is a reasonable question, the answer is sometimes yes, and the thing that decides it is not the card. It is what your reader on the gatepost is listening for.
There are two different radios, and they cannot hear each other
Access control in the UK splits broadly into two camps. Older proximity systems run at 125 kHz - low frequency. If your fobs are the small hard plastic teardrops on a keyring and the system has been in since the mid-2000s, that is very likely what you have. EM4100 and HID Prox are the two names you will see on a datasheet.
Newer systems, and everything a phone can talk to, run at 13.56 MHz - high frequency. That is where MIFARE lives, and it is also where the NFC in every modern phone lives. It is the same band, which is exactly why a single card can do two jobs at all.
The two do not interoperate. Not partially, not with the right card, not at all. A 13.56 MHz card held against a 125 kHz reader does nothing, and no amount of choosing a better card changes that. This is the single fact that decides whether the idea is worth pursuing on your site, and it is worth five minutes finding out before anybody orders anything.
If your fobs are 125 kHz, one card cannot do both jobs. That is a property of the radio, not of the card you bought.
How to tell which one you have, without guessing
- Look at the reader. The model number is usually printed on it or on the back plate. Search that number and the frequency is on the first datasheet that comes up.
- Ask whoever maintains the system. They will know immediately, and they are the people who have to enrol any new credential anyway.
- Look at what your existing fobs are called on the invoice. EM4100 or Prox means 125 kHz. MIFARE, Classic, DESFire or NTAG means 13.56 MHz.
- Try tapping an existing fob against a phone with NFC on. If the phone notices something is there, it is 13.56 MHz. If nothing happens at all, that is a strong hint it is 125 kHz - though it is a hint rather than proof.
If the answer comes back 125 kHz, you are not stuck - you just need two things rather than one, and a printed QR on a card is still the cheapest way to make the contact half of the problem go away.
What a dual-chip card actually is
It is one piece of plastic with two independent chips in it, and the word independent is doing real work in that sentence. The full specification is published on the dual-chip card page, and it is worth reading before you ask anybody for a quote. One chip is an NFC tag - an NXP NTAG213, 13.56 MHz, ISO/IEC 14443A - encoded with a link to a live contact profile. Tap it on a phone and the profile opens in the browser. No app, on either side.
The other is a MIFARE access credential, supplied as Classic 1K or DESFire depending on what your reader expects. That is the chip your gate is interested in, and it is the one your access provider has to enrol into the system exactly as they would enrol a new fob.
Because the two chips are separate, programming one never touches the other. Re-encoding the contact side does not invalidate the access credential, and re-enrolling the access credential does not change where the tap goes. That independence is the reason the idea works at all.
The questions to put to your access provider
- Does the reader work at 13.56 MHz? If no, stop here.
- MIFARE Classic 1K or DESFire? This decides which card is ordered, and the two are not interchangeable.
- What UID length does the system expect? Classic 1K is typically a 4-byte UID and DESFire typically 7-byte. A system configured for one will not accept the other.
- Can you enrol a credential we supply, or do cards have to come from you? Some systems and some contracts only accept the installer's own stock, and that is a commercial answer rather than a technical one.
Those four answers are the whole decision. With them, a quote takes minutes. Without them, anybody who sells you a card is guessing, and the person holding the guess is you, standing at a gate.
Why we do not stock it
We sold the dual-chip card as a standard product and then stopped, and the reason is worth being straight about because it is not the usual one. Our supplier advised against carrying it in their own words: a very niche product, and it looks visually identical to the standard white PVC cards. That is the problem in a sentence. There is nothing to photograph, nothing that shows a customer why it costs more, and no order was ever placed for one.
So it is made to order rather than stocked. The page is still there, the specification is still published in full, and if your four answers come back right we will quote it. What we will not do is sell you one on the assumption that it works with hardware nobody has tested it against - our Terms say so plainly and this is what that clause is actually for.
The half of the problem you can solve today for nothing
Whatever the frequency turns out to be, the contact half needs no hardware decision at all. A live profile with a QR code can be on the gate, the office door and the noticeboard this afternoon, carrying the daytime line, the out-of-hours number and directions to the correct entrance - and when the out-of-hours number changes, the sign does not. There is more on how that works for sites and marinas, and the weatherproof signage is in the range.
That is usually the more valuable half anyway. The gate only has to let the right people in. The sign has to work for everybody who turns up after the office has shut, which is a larger group and a worse moment to get it wrong.