# RFID key fob, EM4305, programmable

> RFID key fob with EM4305 chip, programmable and rewritable, used in access control and identification systems. Operates at 125KHz frequency, with a read distance of 3-10 cm depending on the reader. Made of plastic with a metal ring, water resistant. Dimensions: 35 x 28 x 4 mm.

- Page: https://sigmanortec.ro/en/rfid-key-fob-em4305-programmable
- Price: 4.88 RON
- Availability: In stock; 1-2 zile
- Reference: 9646 · EAN: 5944762034413
- Category: Electronic components > Access Control > RFID Cards and Tags
- Package (shipping data): 0.005 kg
- Updated: 2026-10-19
- Shop: [Sigmanortec.ro](https://sigmanortec.ro/en/llms.txt)
- Prices: RON, VAT included; prices and stock as of 2026-10-22 02:22 (Europe/Bucharest)

## Description

RFID key fob with EM4305 chip, ideal for access control and identification systems, rewritable tag for easy cloning or data update. It operates at 125KHz, has a reading distance of 3-10 cm depending on the reader, is waterproof and made of plastic with a metal ring for secure attachment. Dimensions 35 x 28 x 4 mm.
The RFID key fob with EM4305 chip is a passive 125 kHz transponder that can be written and rewritten, intended for access control, identification, and attendance tracking systems. Unlike fixed-code key fobs, its contents can be reprogrammed with a compatible writing device, making it suitable for replacing lost keys, updating data, and testing in projects with low-frequency RFID readers.
The EM4305 chip produced by EM Microelectronic has a 512-bit EEPROM memory, organized into 16 words of 32 bits, and a factory-programmed unique 32-bit identifier (UID). The chip supports 32-bit password protection for reading and writing, and memory words can be locked so that they become read-only. Data can be transmitted with Manchester or bi-phase encoding, and memory commands and updates are sent by modulating the 125 kHz magnetic field. Detection distance is 3 - 10 cm and depends on the reader used.
Among the main features are the blue plastic housing, drop shape, with attachment hole, the two included metal rings for fastening to a key set, and water resistance. The key fob has no battery and does not require external power, because the chip is powered from the magnetic field generated by the reader or writing device.
The key fob is compatible with 125 kHz RFID readers, programmers, and copiers that support the EM4305 chip. Compatibility with a specific access system depends on the data format expected by the reader, so check the documentation of the equipment used.
Specifications:
Power supply: Passive, from the reader's magnetic field
Chip: EM4305
Rewritable: Yes
Operating frequency: 125 kHz
EEPROM memory: 512 bits (16 words of 32 bits)
Unique identifier: 32-bit UID
Protection: 32-bit password for read and write, memory word locking
Data encoding: Manchester and bi-phase
Detection distance: 3 - 10 cm, depending on device
Material: Plastic and metal rings
Water resistant: Yes
Dimensions: 35 x 28 x 4 mm
Use:
Check that the writing device or copier used operates at 125 kHz and explicitly supports EM4305 chips, because not all 125 kHz equipment can write this type of chip.
Bring the key fob close to the reading or writing area of the device, with the flat side facing the antenna, at a distance of 3 - 10 cm, depending on the reader.
Follow the writing procedure indicated by the device manufacturer and keep the key fob still until the operation is complete, then verify the result by reading it.
Do not use the password and memory word locking functions without noting down the password, because a locked word becomes read-only, and a lost password can make the key fob impossible to reprogram.
Mount the key fob in the reader with at least a few millimeters of distance from thick metal surfaces, because nearby metal reduces the detection distance.
For stable results, avoid hitting, bending, and exposing the key fob to high temperatures or strong magnetic fields, and keep the metal rings away from the reader antenna during reading.