RELEASE MECHANISM

Head-mountable devices can include connection and engagement mechanisms that facilitate operation of a head-mountable device with an accessory device. Such connections can provide both mechanical engagement and operable communication between the connected devices. A variable lock of the head-mountable device can distinguish between low-impulse and high-impulse forces applied to one or more connection regions. In the event of a low-impulse force, the variable lock can secure segments of a head engager together so the head-mountable device can remain on the head of the user. Optionally, the accessory device can be disconnected from the head-mountable device. In the event of a high-impulse force, the variable lock can allow segments of the head engager to separate so the head-mountable device can be released from the head of the user.