Knock Detection for Smart Doorbells: Hearing the Visitors You Would Have Missed

The Visitor Behavior We Keep Missing

The courier drops the parcel, knocks twice and leaves. A neighbor knocks on the window in passing. A child is too small to reach the doorbell button... In reality, a large share of arrivals never touches the doorbell. Button-only doorbells miss these visitors — and motion detection cannot tell "someone walked by" from "someone knocked," producing imprecise alerts and notification fatigue.

Knock Detection Closes the Awareness Gap

Adding knock recognition to a doorbell or entry camera lets the device understand visitor behavior:

• wake the video feed the instant a knock occurs — no visit is missed

• upgrade notifications from "motion detected" to "someone is knocking"

• combine with visit logs to form a complete door event history

The End-to-End Workflow

Here is the complete on-device chain for a single knock event:

1. Knock occurs — a visitor raps on the door or window

2. Continuous listening — the doorbell microphone monitors the entrance at low power

3. Event detection — knock-like acoustic features are recognized while footsteps, door slams and wind are rejected

4. Wake and record — the video doorbell wakes up and starts recording

5. Push notification — the user receives a "someone is knocking" alert with live video

6. User response — view live, talk back, use a preset reply, or dismiss

Why Knocks Are Harder to Distinguish Than They Sound

The entrance environment is acoustically busy. Knock-like sounds must be separated from:

Footsteps — — periodic, low-frequency, no sharp transient structure

Door slams — — concentrated low-frequency energy with a different decay pattern

Wind and rain — — sustained noise without event structure

Music beats — — rhythmically periodic, ruled out by periodicity analysis

At the principle level, knock detection is again transient-event analysis: locate the short energy burst first, then separate knocks from other transients by their time-frequency signatures. All processing happens on the device — audio never leaves it.

Platform Compatibility and Performance

Far-field knock detection is supported, sharing the SoC with the camera workload without affecting video encoding or streaming.

Broader Applications

Smart locks — — add visitor awareness to entry devices

Home security cameras — — tapping detection near doors and windows

Unattended stores — — after-hours knock monitoring

Elderly care — — detecting knocking on bed frames or tables as a call for help

Conclusion

Visitors do not always ring the bell — but they always make a sound. Knock detection upgrades a doorbell's awareness from "seeing" to "hearing," so no visit is missed. An online trial with full technical support is available — we welcome your evaluation.