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    STI-3331 Wireless Doorbell Extender — Installation & Operation Manual

    August 31, 2026 3 min read

    Installation and Operation Manual for the STI-3331 Wireless Doorbell Extender, which adds wireless range to an existing wired doorbell via the STI-3353 chime receiver.

    💾 Download Original PDF
    Full text manual (for reference)

    Installation and Operation Manual for the STI-3331 Wireless Doorbell Extender — a transmitter that wires into an existing house doorbell circuit and sends a wireless signal to an STI-3353 chime receiver, letting you add wireless range/notification to a wired doorbell without replacing it.

    Features

    • Up to 500 ft. operating range (line of sight)
    • Low and high volume setting on receiver
    • Low battery alert
    • FCC and IC certified
    • 433 MHz

    Works with the STI-3353 Wireless Chime Receiver.

    Wire Connections

    The Extender Sensor connects to the existing doorbell's screw terminals via fork-shaped connectors:

    • Black — 'Front' screw
    • Brown — 'Rear' screw
    • Red — 'Trans' screw

    Installation

    1. Ensure the existing house doorbell has no power going to it (disable the circuit).
    2. Use double-sided tape to mount the Extender Sensor inside or outside the house doorbell box.
    3. Slide the Extender Sensor's fork-shaped connectors onto the house doorbell's screws. Do not disconnect existing doorbell wires.
    4. If the house doesn't have a 'REAR' doorbell, tape off the brown wire connector and leave it disconnected.
    5. Restore power to the existing house doorbell.
    6. Plug the receiver into an outlet.
    7. Press the pairing button on the receiver — it will make a tone.
    8. Press the front doorbell button. You should hear the existing doorbell sound plus a tone from the receiver acknowledging pairing success. (The back doorbell button will automatically pair if used.)
    9. Press the pairing button on the receiver again to exit pairing mode.
    10. The front doorbell sounds "ding-dong" and the back doorbell sounds "ding." Sounds cannot be changed.

    Pairing the Receiver with the Extender

    • Plug the STI-3353 receiver into a standard 120 VAC outlet.
    • Press the pairing button on the bottom of the receiver — it will make a tone.
    • Follow the installation steps above to finalize pairing.

    Important Notes

    • The Wireless Doorbell Extender Sensor is powered directly by the existing house doorbell circuit (16 VAC, 10A) — no batteries required.
    • The Extender wires directly into the existing doorbell system, not into the transformer.
    • This product may not work properly with some door chimes that play melodies or use batteries.
    • Mounting the transmitter on a metal surface will reduce range — a ½" wood spacer may help resolve this.

    Troubleshooting

    Problem Fix
    Extender does not sound Check that all wires to the chime terminal strip are tightly connected to the correct screws. Make sure the outlet is functioning. Confirm the receiver and sensor are within the 500 ft. operating range (range may vary by environment). Verify minimum outlet power to the receiver is 110 VAC. The extender may not be compatible with all doorbells, especially digital/musical doorbells. Verify power to the existing doorbell is 16 VAC, 10VA.
    Receiver sounds randomly Make sure the original doorbell button isn't stuck.
    All transmitters play the same tune Sounds for front and back doors are fixed and cannot be changed. Make sure the black and brown wires are not shorted together.

    Regulatory

    This device complies with Part 15 of the FCC Rules and Industry Canada license-exempt RSS standards. Operation is subject to: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

    STI-3331 — FCC ID: TXL3331, IC: 6335A-3331

    Changes or modifications not expressly approved by Safety Technology International, Inc. could void the user's authority to operate the equipment.

    Warranty

    Safety Technology International, Inc. warrants to the original consumer/purchaser that this product is free of defects in material and workmanship under normal use for one (1) year from the original date of purchase. Electronic warranty form at www.sti-usa.com/wc14.

    Contact

    Technical Support: 800-888-4784

    Safety Technology International, Inc., 2306 Airport Rd, Waterford, MI 48327, USA — Tel: 248-673-9898, Fax: 248-673-1246, info@sti-usa.com, www.sti-usa.com

    Safety Technology International Ltd, Taylor House, 34 Sherwood Road, Bromsgrove, Worcestershire B60 3DR, England — Tel: +44 (0)1527 520 999, Fax: +44 (0)1527 501 999, info@sti-europe.com, www.sti-europe.com