Embodiments relate to an insertion device that includes: a plunger coupled with a lock collar. The insertion device houses contents including: a striker including self-locking striker snap arm(s) where the striker is kept from firing by a striker spring captured between the plunger and the striker when the insertion device is in a cocked position; a sensor assembly; and a needle carrier that holds a piercing member, the needle carrier captured between the striker and a needle carrier spring where a self-releasing snap(s) keeps the needle carrier cocked, where the plunger prevents the self-releasing snap(s) from repositioning and releasing the needle carrier. The striker fires the needle carrier such that the self-locking striker snap arm(s) are positioned to allow the striker to snap down. The needle carrier is then retracted when the user releases the plunger and the piercing member is encapsulated within the insertion device.