RFID Proximity Fobs

What is a proximity fob?

A proximity fob is a 125 kHz low-frequency (LF) RFID key fob that a proximity reader reads when it is held a few centimetres away. It is the keyring credential for door entry, car-park barriers, lifts and time-and-attendance terminals on existing "prox" systems, and it is chosen by one rule: the chip and the ID format must be ones your reader and access controller already accept. Identify those first, then choose the housing and the printed number.

The fob has no battery. The reader's 125 kHz field powers the chip through a small copper coil inside the housing, and the chip answers with its identification code. The reader converts that code into the output the controller expects, and the controller decides whether the door opens. Because the fob only carries an ID, almost every compatibility question on this page is about the chip family and how the number is formatted, not the shape of the fob.

Proximity fob specification at a glance

Which 125 kHz chip should a proximity fob use?

"125 kHz" names a frequency band, not a chip. Several chip families share the band, and a reader built for one does not necessarily decode another. Match the chip to what your reader decodes and to whether anyone needs to write to the fob after delivery.

If your installer's specification says "EM", "EM4100", "EM-Marin" or "TK4100", the EM4200 fob is the standard answer. If the fob must carry a number you choose, or match a site code already used on your cards, order T5577 or EM4305 and tell us the format. T5577 and EM4305 use different programming commands, so pick the one your own writer supports if you will encode fobs yourself. The same chips are available as cards; see 125 kHz RFID cards when staff need a badge and a fob on the same system.

EM4100 key fobs: what the ID number contains

An EM4100-format fob, EM4200 included, sends 40 data bits in a repeating 64-bit frame, which the EM4200 card page lays out bit by bit.

Readers and software show those 40 bits in different ways, which is why two people can read the same fob and quote different numbers. The chip's number does not change; only its representation does.

ID formats: facility code, card number and Wiegand 26-bit

The access controller defines the format, not the fob. A reader wired to a controller usually sends the ID as a Wiegand message, and the controller only accepts messages of the length and structure it has been set up for. The number printed on the fob is useful only if it is printed in the same representation that your software shows when a fob is enrolled.

Wiegand 26-bit leaves only 65,536 card numbers per facility code, so duplicates between sites are possible. If your system uses a fixed facility code, a read-only EM fob cannot be made to carry it; order T5577 or EM4305 fobs pre-encoded with your facility code and number range instead, and we print the same numbers on the housing.

Proprietary 125 kHz credentials use their own modulation and data structures, which differ from EM4100. The T5577's datasheet gives it FSK, PSK, Manchester, Bi-phase and NRZ output at a choice of data rates, but it names no proprietary credential format, and we do not claim compatibility with any. A fob configured to the format your reader expects is proven only by a sample test on your reader and controller; confirm the result with your system provider before a volume order.

Housings: ABS teardrop, epoxy, leather and more

The housing decides how the fob looks, how it survives a keyring and how it is marked; it does not change the chip or the format. Most access-control projects use a standard ABS shape, and other materials are chosen for branding, gifts or harsher use.

Colour-coding is an easy operational win: different colours for residents, staff, cleaners and contractors make a wrongly issued fob visible at a glance. For outdoor gates, pools or wash-down areas, ask for the water resistance of the specific housing, because ratings differ between moulds and materials and are confirmed per product rather than assumed. More shapes and dual-frequency options are listed under RFID key fobs.

Printed or laser-engraved numbering and logos

• Laser engraving: a permanent mark in the ABS surface, the usual choice for ID numbers because it does not wear off on a keyring.
• Pad or screen printing: one or two spot colours for a logo or short text on the flat face.
• UV printing: full-colour artwork on flat areas of the housing.
• Epoxy dome: full-colour print sealed under clear resin, for fobs where artwork matters more than the housing shape.
• Number list: a file in Excel, CSV or XML pairing each printed number with the fob's chip ID comes with every numbered order, so fobs can be enrolled in bulk instead of one at a time at a door if the controller software accepts an imported list.

Tell us the representation to print (decimal, hex, or facility code and card number), the number of digits and whether leading zeros are kept. On read-only EM fobs we print either the number read from each chip or a running number of your choice; on rewritable fobs we encode the number range you specify and print the matching numbers.

Can proximity fobs be copied?

Yes. A 125 kHz proximity fob sends its ID to any compatible reader with no authentication, so a handheld copier can read it and write the same ID onto a rewritable T5577 blank. A read-only EM4200 cannot itself be rewritten, but that does not stop its number being copied onto another fob. Password protection and block locks on a T5577 or EM4305 prevent that fob from being overwritten; they do not stop it being read and duplicated.

That makes proximity fobs a sensible match for existing LF readers and lower-risk doors, not for sites where a copied credential carries real cost. For higher security, move to 13.56 MHz fobs or cards on MIFARE DESFire, which authenticate with keys held by your system; the RFID key fob page covers DESFire fobs and dual-frequency fobs that carry an LF and an HF chip for sites upgrading readers in stages. We supply blank and pre-encoded fobs for the system owner's own issuing and do not duplicate credentials for systems the buyer does not administer.

Blank, pre-encoded or fixed ID: how are proximity fobs delivered?

• Read-only EM fobs: the ID is fixed at chip manufacture and cannot be chosen, so the printed number is the chip's own or a running number, and the number list pairs the two.
• Blank rewritable fobs: T5577 or EM4305 for installers who encode on site with their own writer.
• Pre-encoded rewritable fobs: we write the format, facility code and number range you specify, read each fob back to check it, print matching numbers and include a data report with the order; see the RFID encoding service.
• Protection settings: passwords and block locks are applied only if you ask for them, and only after the format has been approved on your sample, because a locked block cannot be corrected later.

How to check a proximity fob against your system

• Confirm the frequency. A 125 kHz fob is not detected by an NFC phone; if a phone reads your current fob, it is 13.56 MHz and this page is the wrong product.
• Send the reader or controller model, or a working fob, so the chip family and format can be identified.
• State the output the controller uses: Wiegand 26-bit, 34-bit, keyboard emulation or another format, plus any facility code.
• Test free samples on the actual reader and controller, including enrolment in the software, not only a beep at the reader.
• Approve the chip, format, printed number layout and housing, and keep that approved sample as the reference for repeat orders.

Ordering, samples and lead time

Proud Tek has manufactured RFID and NFC products in Shenzhen since 2008. Strong chip supply channels and our own production and quality control let us quote competitively against your chip, housing, marking and quantity, rather than against a generic catalogue price. A useful inquiry includes:

• Chip or reader model, and the output format and facility code if known.
• Housing shape, material and colours, with artwork for logos.
• Numbering: representation, digits and number range.
• Blank, pre-encoded or fixed-ID delivery, and any password or lock requirement.
• Quantity, destination and target delivery date.

Standard samples are free and can be requested through the sample pack; customised samples carry a setup fee confirmed in the quotation. Standard products generally ship in 2–3 weeks, and large orders are scheduled individually. MOQ, unit price and freight are confirmed in the quotation for your specification and destination. We reply within one business day and quote within one business day of a workable inquiry; send the details through the contact page. Certificates and supply terms are on the RFID card and NFC tag manufacturer page, and the RFID key fobs for access control guide covers reader, controller and lift planning.

Chip references: EM Microelectronic EM4205/EM4305 datasheet, Microchip ATA5577C datasheet and NXP HITAG 2. Chip documentation describes the IC; the finished fob specification is confirmed with your sample and quotation.