The Sonic Stun Weapon, also called the "stunner", is a hand-held weapon designed by Henry Foss. It uses sonic sound waves to temporarily stun the victim. When Dr. Helen Magnus used it on John Druitt, she had to shoot him three times to bring him down but the final shot stopped his heart.
Stunners have also been used as offensive weapons on several occasions, for example when Helen Magnus is forced to shoot a mercenary who was attempting to capture an abnormal.
Stunner batteries are removable, as shown by Henry using the stunner battery in order to power the emergency lighting in a destroyed Cabal bunker. They also appear to have ajustable power settings as shown during Nikola Tesla's rescue from a army of multipedes; the shot from the stunner suddenly changes from blue to orange, and is capable of bringing down a rock ceiling. It is unknown wether Henry put this in intentionally.
By 2011 the mark II sonic stun weapon was designed by Henry Foss. Later Helen Magnus and Henry Foss used the mark II sonic stun weapon inside Area 51 after tracking an Abnormal fugitive, and discovers that Tesla is the head of a secret research lab for a Homeland Security agency that conducts tests on Abnormals. 
Later that year the Sanctuary team used the mark II sonic stun weapon against a humanoid abnormal with a naturally armored body in the Sanctuary, it had no effect on the abnormal until Helen used a super sonic stun weapon.