Some of latest doorbell cameras offer a pre buffer feature that records several seconds of activity prior to when a motion sensor is triggered or the doorbell button has been pressed so you can see what happened just before an event. Many home security systems offer video doorbells as add on components, but these devices typically do not work on their own and must be connected to a system hub. However, they usually interact with other system components such as door locks, sirens, and lighting. If you want a standalone smart doorbell that will work with other smart devices in your home, look for one that supports the IFTTT If This Then That internet service. With IFTTT you can easily create mini programs, called applets, that let IFTTT enabled devices interact with each other. For example, you can create an applet that tells a Wemo Smart Switch to turn on when a Ring Doorbell is pressed, or have a D Link siren sound when an August Doorbell Cam senses motion.