A wellbore assembly includes a cable and a wellbore tool. The wellbore tool is coupled to the downhole end of the cable. The wellbore tool includes a housing, one or more sensors, a packer, and a controller. The one or more sensors are coupled to the housing or to the cable or both. The sensors detect one or more parameters of the wellbore tool or the cable or both. The controller is coupled to the housing. The controller is electrically coupled to one or more sensors and is operationally coupled to the packer. The controller determines, with the wellbore tool parted from the cable and based on information received from the one or more sensors, an indication of the wellbore tool in free fall. The controller activates, based on the determination, the packer to expand the packer and set the wellbore tool on a wall of the wellbore.