Back in 2013, we first heard about SCP Marine Innovations' X2 Underwater Jet Pack, which allowed users to "fly" underwater like Aquaman. It consisted of two forearm-mounted thrusters, each of which were hard-wired to a battery pack on the user's back. Well, German inventor Un-Yong Park has created something along the same lines, but that's considerably simpler – it's called the Scubalec.
The device is worn on the user's left forearm, and consists of two cylindrical thrusters and a battery. Each thruster uses an impeller to draw water in through an opening in the top, then expel it out a nozzle in the back – Park compares it to the method in which a squid propels itself through the water.
Users control the amount of thrust via a thumb-operated throttle switch, and steer simply by changing the direction in which their arm is pointing. From the looks of the video at the bottom of the page, its maximum speed is roughly equivalent to what users could manage by kicking their legs – so you'd use it to save your energy, and not necessarily to go faster.
One charge of the removable 7,500-mAh lithium-ion battery should reportedly be good for about 10 to 12 minutes of continuous use.
Park is currently raising production funds for the Scubalec, on Kickstarter. A pledge of €277 (about US$297) will get you one, when and if it's ready to go. The planned retail price is €399 ($427).