There are 3 unlockable weapons, Micro Missiles, Ultra Beam and Reflect Shield. you're only able to choose from these weapons if you've got Beat Hazard Ultra

BH weapon 1

Micro Missiles

Micro Missiles: Fires a hail of homing missiles. Each missile will target the highest threat on-screen. Incoming enemy missiles are the highest threat followed by Bosses and then Mini-Serpents, Repulsars and Stalkers.
BH weapon 2

Ultra Beam

Ultra Beam: Fires a concentrated beam of death and destruction. With a good aim this weapon can do massive damage. You can take out a boss turret or a string of ships in one blast. Good for path clearing.
BH weapon 3

Reflect Shield

Reflect Shield: This is the awesome shield of awesomeness. Not only does this shield protect you from all impacts it will deflect any incoming projectile and turn it against the enemy! Used on a swarm of missiles can cause devastation to the enemy hordes.

BIG TIP: One important tactic to remember is that all three weapons are stackable. That is if you fire the shield 5 times quickly the game will stack 5 shields one after the other. Try it, it’s useful!