125kHz RFID Keyfob (TK4100) – Proximity Key Tag for Access Control

125kHz RFID keyfobs (also called 125kHz RFID key tags or proximity key fobs) are read-only low-frequency (LF) credentials built around the TK4100 chip, fully compatible with the EM4100 / EM4102 / EM4200 protocol family. Each fob sits in a rugged, waterproof ABS shell with a keyring hole and carries a unique, factory-locked 64-bit ID that your reader uses to identify the holder. Because the chip is read-only and cannot be altered after encoding, this is the cost-effective workhorse for high-volume access control, time & attendance, parking and membership systems that need a stable, tamper-resistant identifier rather than on-tag data storage. For projects that require field re-encoding, a T5577 / EM4305 rewritable keyfob is available on the same form factor.

This 125kHz keyfob works with virtually any access controller, time clock or USB enrollment reader that supports the EM4100 / EM410x protocol - standalone door controllers, Wiegand-26/34 access panels, time-and-attendance terminals, and EM-format desktop readers used for batch enrollment. It is the proximity counterpart to our 125kHz EM4100/TK4100 key fobs and matching 125kHz TK4100 cards.

Important notes before you order:

• It is a 125kHz LF credential and will not work with 13.56MHz (MIFARE/NFC) readers - confirm your reader frequency first. Need both? See our dual-frequency key fobs.
• The TK4100 is read-only. If your system re-encodes credentials in the field, choose the rewritable T5577/EM4305 version.
• 125kHz EM keyfobs are not encrypted; for high-security sites pair them with a secure controller or upgrade to an encrypted 13.56MHz credential.
• We can pre-encode each fob to your existing UID format and number range, so new fobs integrate directly with your database.

How to choose the right version: ① confirm reader frequency is 125kHz/EM-compatible; ② read-only TK4100 for a fixed ID, T5577/EM4305 if you re-encode; ③ send us your current UID format for seamless integration; ④ add logo/color for staff or member identification. Unsure which fits? Send your reader model and we'll confirm compatibility before you order. Background reading: choosing the right frequency for RFID keyfobs.

What the specs mean for your deployment: the 64-bit read-only ID is a permanently locked identifier - changeable data such as balances or access levels live in your software, not on the fob. The 125kHz / ISO/IEC 18000-2 band gives a short read range with strong tolerance to metal and moisture, which is why LF remains the standard for rugged access credentials, while the 2–5 cm range means a deliberate "tap" that reduces accidental reads. The waterproof ABS body and -20°C to +70°C range suit outdoor gates and humid or industrial sites.

• Building & facility access control - apartments, offices, factories and gated communities, one tamper-proof fob per resident or employee.
• Time & attendance - staff tap-in/out at clock terminals; the fixed UID maps to each worker in HR/payroll software.
• Gyms, clubs & spas - durable, waterproof membership fobs that survive locker rooms and pool areas.
• Parking & turnstiles - short-range credentials for barrier and gate control.
• Hotels & co-living - automated check-in/check-out and back-of-house staff access.
• Asset & equipment check-out - fobs attached to tool kits, vehicles or keys for accountable hand-over.
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As a factory-direct manufacturer we tailor 125kHz keyfobs to your project. Full options and artwork support are on our OEM / ODM customization page.

Typical workflow: inquiry → spec confirmation & quotation (within 24 h) → free sample → artwork & encoding sign-off → mass production → QC → shipment.

• Manufacturer, not a reseller - our own factory in Hunan and QC office in Shenzhen control quality and cost from chip bonding to final inspection.
• Quality & compliance - CE-marked and produced under an ISO 9001-aligned quality system, with RoHS material options on request.
• Consistent supply - stock available for non-customized fobs; predictable lead times for repeat OEM orders.
• Proven RFID standards - built to the ISO/IEC 18000-2 LF air interface, using the widely deployed EM Microelectronic EM4100-compatible chip family.
• Buyer-friendly terms - free samples, 24-hour quotation, flexible MOQ for distributors, integrators and OEM brands.
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