Modular accessory systems for wearable devices

Systems and devices are disclosed herein that provide or relate to modular accessory devices for a wearable device, such as a glasses-style head-mountable device (HMD). Illustrative systems may include a first frame component having an accessory slot accessible via an entry point on a transverse surface of the first frame component, a second frame component movably coupled to the first frame component, and one or more accessory devices that each have a slot-mating feature shaped for insertion into and removal from the accessory slot via the entry point. The second frame component may be movable between a first position in which the second frame component blocks access to the entry point, and a second position in which the second frame component allows access to the entry point.