Home security systems may become more advanced, but that doesn’t mean they can’t be simple. There is now smart lock technology that grants residents access by listening to the way they knock.
A recently published patent application from Virginia-based Alarm.com features a device with three major parts: a proximity sensor, a microphone, and a monitor control unit.
A diagram illustrating an example system for door knock access control.
The proximity sensor is installed at the door of a property, and may be based on infrared, laser, radar, sonar, or LiDAR. It may be programmed to detect people within a certain distance, and subsequently activate the monitoring system’s microphone.
Before the monitoring system becomes operational, the microphone will be used to set a knocking pattern, which may factor in the number of knocks, their volume, and the time between each one. A resident or owner of a property pre-records this knocking pattern much like setting a passcode for any digital lock.
Whenever the proximity sensor is tripped, the microphone begins to listen for knocking patterns. It may achieve this with assistance from a vibration sensor, which measures amplitude, frequency, and time duration of vibrations.
The patent application states that by installing more than one microphone and/or more than one vibration sensor around a single door, the monitoring system can triangulate where knocking sounds are produced. This adds a level of accuracy by filtering out inputs generated too close to the ground (generated by animals) or too far from the system (generated from a neighboring door).
Besides handling the interactions between the proximity sensor and the microphone, the monitor control unit is responsible for matching the detected knocking patterns with those stored in the monitoring server. These must satisfy a level of similarity, referred to as the “matching threshold,” to grant a user access. Upon detecting a match, the monitoring system may notify a resident or turn on a porch light.
Alarm.com notes that its knock-sensing lock would likely be implemented as an additional layer of security on top of a door access code. For example, a door may only present an option to input a code after matching a knocking pattern. Inversely, receiving a correct access code may trigger the microphone to listen for knocks. In this case, the invention would no longer require a proximity sensor.
The featured patent application, “Door Knock Access Control”, was filed with the USPTO on December 30, 2020 and published thereafter on July 15, 2021. The listed applicant is Alarm.com Incorporated. The listed inventors are William Wireko Mensah, Daniel John Koniar, Liyu Yao, Martin Logan Elliott, and John Zhang.