Now, before you read: I'm not fully experienced with the Security Guard class. The only reason I'm making this is because I'm starting to feel how Security Guard was supposed to be used.
Cameras. I saw someone point while they had cameras up, highlighting the killer. I wanted to figure it out myself, and did. Apparently, for those who wants to get Security Guard, you can click on objectives like generators and batteries to highlight them, making them easier to find. The biggest thing, though, is that you can also click on the killer to highlight them too, which can REALLY help with assisting survivors and knowing when to charge your tazer. There's also the fact that the cameras autoswitch to the one where you can see the killer when bringing them up, so you can easily and quickly highlight where they are. I've managed to assist a fighter in one match, despite being at low HP. The weapon I was using to help is:
Tazer: Now, this weapon needs to be used carefully. This is why you have cameras in the first place: To predict where the killer will be so you can hit a high charge of your tazer. Even shooting the killer with the tazer at a distance right after you start charging already prevents most moves but M1 from being used, including ranged ones and other powerful abilities like Axe Throw, Ennard Grab, and Drill. It's also supposed to be used in teamwork: Slowing the killer down for your teammates to run away, not to slow down the killer for YOU to run away, because you also get slowed down... but a good solo use case is if you're low on stamina, which you can get free stamina regen, if I remember, but you're basically also giving the killer the time to let their cooldown go down further. You're supposed to stay behind for others to survive. Killers can't really do anything if they get tazed and the oneshot survivor is out of M1 reach, so make sure that happens to keep your teammates alive.
The only problem I have with Security Guard is this trend I've noticed where even a killer who knows what to do... not an experienced one, not a good one, just one who knows what they're doing... that they target the FUCK out of Security Guards, only making more sense to team with a Security Guard as a survivor, or to team with a fighter as a Security Guard.
Imo, Security Guard is a REALLY great class... it's just that I don't see much people use the class properly. I feel like this is gonna be a hot take because of how annoying Security Guard can be if you're with no one else and the killer is chasing you.