information when calculating routes. In the event that devices have been moved and the previously stored signal strength is wrong, the controller may issue a new route resolution through one or more explore frames. Each Z-Wave network is identified by a Network ID, and each device is further identified by a Node ID. The Network ID (also called Home ID) is the common identification of all nodes belonging to one logical Z-Wave network. The Network ID has a length of 4 bytes (32 bits) and is assigned to each device, by the primary controller, when the device is "included" into the Network. Nodes with different Network IDs cannot communicate with each other. The Node ID is the address of a single node in the network. The Node ID has a length of 1 byte (8 bits) and must be unique in its network. The Z-Wave chip is optimized for battery-powered devices, and most of the time remains in a power saving mode to consume less energy, waking up only to perform its function. With Z-Wave mesh networks, each device in the house bounces wireless signals around the house, which results in low power consumption, allowing devices to work for years without needing to replace batteries. For Z-Wave units to be able to route unsolicited messages, they cannot be in sleep mode. Therefore, battery-operated devices are not designed as repeater units. Mobile devices, such as remote controls, are also excluded since Z-Wave assumes that all repeater capable devices in the network remain in their original detected position. Security Z-Wave is based on a proprietary design, supported by Sigma Designs as its primary chip vendor, but the Z-Wave business unit was acquired by Silicon Labs in 2018. In December 2019, Silicon Labs announced that it would release the Z-Wave specification as an open wireless standard for development to be certified by the Z-Wave Alliance. An early vulnerability was uncovered in AES-encrypted Z-Wave door locks that could be remotely exploited to unlock doors without the knowledge of the encryption keys, and due to the changed keys, subsequent network messages, as in "door is open", would be ignored by the established controller of the network. The vulnerability was not due to a flaw in the Z-Wave protocol specification but was an implementation error by the door-lock manufacturer. On November 17, 2016, the Z-Wave Alliance announced stronger security standards for devices receiving Z-Wave Certification as