button is released, to continue playing the doorbell song. This can be achieved in one of two ways. For simple single-pole, single-throw doorbell buttons, the chime device employs a rectifier diode and ballast capacitor at the voltage input stage of the circuit. Upon pressing the doorbell button, power is connected through the rectifier diode or series of rectifier diodes called a full wave rectifier, which allows the current to flow in only one direction, into the ballast capacitor. The ballast capacitor charges at a rate far greater than the rest of the circuit needs to complete a given song. Once the button is released, the capacitor retains the charge and maintains power for a short duration to the rest of the circuit. For mixed wireless and wired input doorbells, a special doorbell button is needed to maintain power continuously to the doorbell chime. The circuit is similar to the one above, except that the rectifier diode is now moved into the doorbell button housing. Pressing the doorbell button allows both negative and positive sides of the AC power signal to flow into the circuit, while releasing the button only allows either the positive or negative side to flow into the circuit. By differentiating the full and half wave signals, the doorbell is able to function as it does in the previous wired case, while also providing continuous power to the doorbell for other purposes, such as receiving wireless doorbell button input. Smart doorbells With the rise of the Internet of Things in the 2010s, a number of internet-connected bell systems, known as smart doorbells have appeared on the market. Popular systems include the Ring doorbell, Vivint Home Security doorbell, and the Nest Hello. These consist of a single unit which is located in place of the traditional push-button, and in addition to a physical button, contains a high-definition camera, passive infrared sensor and Wi-Fi capability. The device is connected to the home Wi-Fi network, and notifications of a button-press or detected movement are pushed to a paired smartphone or other electronic device such as a tablet. When a notification is received, the user will typically see a live video stream from the smart doorbell, showing who is at the door and potentially allowing a 2-way audio conversation. The devices can be powered by an internal battery, or they may use the existing bell wiring for continuous power. The video is