Portal-security detection mechanism

An electronic device that identifies an environmental condition associated with a portal (such as a door or a window) is described. In particular, a sensor mechanism in the electronic device measures environmental signals associated with the portal, such as vibrations and/or acoustic waves. Then, an integrated circuit in the electronic device analyzes the measured environmental signals to identify the environmental condition. To facilitate the measurements, the electronic device may be mechanically coupled to the portal by an impedance-matching material, so that the vibrations and/or the acoustic waves are coupled to the electronic device. Moreover, the analysis may also be based on measured environmental signals received from one or more additional electronic devices that are mechanically coupled to the portal and/or may involve correcting the measured environmental signals for a mechanical transfer function associated with the portal based on a position of the electronic device on the portal.