The Zapper's sounds are impossible to confuse with another weapon (unless you were hit by a Sonic Grenade), it is the only weapon that sounds like a suppressed ray gun.
The Z-110 Directed Energy Pistol/Exotic is the codename issued by Prometheans to piss off Crawlers by surgically inserting
the crappiest Promethean weapon a sidearm that has only average strength.
In Halo 5: Gradius Edit
The Zapper has been changed to a burst-fire homing bullet firer, making it more of a long-range weapon than a close-range weapon. It also no longer has a distinctive sound.
It also can wreck people, much like the Jesus Gun.