I was at work and noticed something peculiar about a back box with a Gentex Commander, It had the wire from the door sensor running through it. The knock out for conduit had a rubber flap on it used for the wiring… So is this the correct way and/or is it a code violation?
I wouldn’t be the person to tell you but I would think that unless it is something like 120 VAC going through the sensor it would just be a bad installation job
Low voltage is allowed to share the same conduit and boxes and it is not uncommon for that to happen. Most of the time anyway, the same company is installing the fire alarm and burglar alarm systems. You don’t want 120VAC mixed in with 24VDC - BUT they get away with it when you look at things like waterflow switches where someone wired up one side of the switch to the 120VAC electric bell and the other side to the 24VDC alarm panel.
Code violation, probably not (especially when burglar alarms are rarely inspected), but there are better more professional ways to pull this off.
The trouble is it is hard to surface wire a door contact and make it look nice, though, because of how small they are. Yes there are better ways to do this though.
Exactly what I said 
I actually came across this today at a local high school and reminded me of this thread! This looks much better and a more beefier door contact too (although the strapping could have been done a little neater). The problem with the door contact the OP posted is that they will easily break as soon as someone knocks something up against the door jamb. Not to mention the wire is not protected and looks like it is only held in place with a single T18 staple and easily pulled out. The picture I’ve posted, the door is the exit door for the maintenance receiving area and will probably last for years, even if struck with something. Personally, any door contact should be of good quality, especially surface mounted. And surface mounted magnets should be spaced off steel doors as much as possible. I’ve seen companies install self stick mini contacts on doors (which are really meant for vinyl windows) and they have nothing but problems and false alarms with them.
I understand the concern for how durable the door contact in the picture is…but the door is rarely used and if so, for long term storage in the basement. Again agreeing with the rest of the posters: It is certainly not the best option but seems to suffice for where the door is and what it’s used for.
I’m trying not saying there is anything wrong with that door contact in particular, personally, I just like using good quality contacts when it comes to commercial installations like that. Door contacts take a lot of abuse. One thing that’s got me about the security burglar alarm industry is there seems to be no real uniformity within the industry. I believe NFPA was thinking about making a code standard for burglar alarms but I might be mistaken. I know this is getting off topic so I’ll keep it short, but some things that seem to bug me are:
Sirens mounted right above keypads (trying to silence a screaming siren that’s 6’ from your ear is bothersome)
Drilling into vinyl windows to flush mount contacts
Running exposed wire over easily fishable hollow walls or cavities (staples into drywall as a bonus)
Inaccessible splices inside walls
Drilling 1/2" hole into the back of a motion detector for a 1/8" diameter wire and not sealing it up