Looking for some fun ways to protect your NPC’s shops? Here are 9 D&D security systems you can use in your campaigns:
1. Tin Cans
System Security Level: 0.5/5
System Description: Now these may not look like much but hear me out. They’re cheap. You just need to eat what was inside them first. They’re eco-friendly. Not only are they not made of plastic but you’re also reusing something you would have just thrown away. Not to mention you could easily string up dozens of these around your shop and your home for a cheap, easy and affordable security system. You could even paint them fun colors or paint them to blend in with their surroundings to not alert creatures that are visiting your establishment during business hours or visiting your home for tea. Imagine if it were fun colors, what a great conversation starter it would be! “Wow, Barbara! Are those baked beans?!”
How it Works: All you need are empty cans and string. You’ll need to set them up each evening and be close by to be alerted of intruders. This security system is best suited for homes or places where you sleep. For the best results you will need to string together six to twelve cans above your closed door. When someone enters the area the tin cans will chime loudly alerting you of their presence. This may also spook local wildlife, babies and your pet.
System Secret: If an intruder were to be made aware of your tin can system they might just open your door slowly. Not triggering the cans thus not alerting you of their intrusion. Also, if you don’t store your cans in a secure location they could be stolen forcing you to quickly eat more canned goods to make your system again.
2. An Invisible Body Guard
System Security Level: 2/5
System Description: Are YOU magically inclined? When you hire your next bodyguard for your store or home, consider making them invisible! This smple trick can provide extra protection without alerting your customers of your security.
How it Works: You will need to hire some good muscle. Someone who is ok with having spells cast upon them. If you have the extra coin you might be able to hire guards that possess the ability to cast this spell. If not, grab an invisibility scroll or cast invisibility using your own spell. Once you’ve figured out how and who it’s a simple process of finding where they’re going to stand for the day, casting the spell and that’s it!
System Secret: An active detect magic will give this security system away. If a patron were to walk in with that and you happen to place your guard in plain sight, they would see an outline of a figure in your store.
3. Silent but Deadly
System Security Level: 3/5
System Description: For those nights when you don’t want to worry about the shop AND you don’t want to hire a guard, why not fill your shop with poisonous gas!
How it Works: Simply stuff a rag under the door and close all the windows, mix up a batch of poison to diffuse throughout the store and head on home! Quickly. Make sure to give yourself ample time to air the place out before opening up the next day, and also to have the bodies of any would-be thieves disposed of!
System Secret: Those of a hearty constitution may be able to hold their breath. There has also been talk around the guilds of some newfangled air filtration masks. It, of course, would also be possible to break a window and let the gas escape before entering – but the thieves would have to know the gas was there first!
4. Forget me not? More like forget me NOW.
System Security Level: 4/5
System Description: Not likely that anyone will steal from you if they can’t remember why they entered the shop in the first place! Steal unsavory characters’ memories from them by befriending critters from the temporal planes!
How it Works: First you have to lure a large group of togrofs to your shop. Should be easy right? You have plenty of doors and windows! Then simply make sure that they have full run of the place when you’re closed, and they’ll make any potential thief forget why they came there entirely!
System Secret: Strong burst of wind (such as those from a fan) can easily push these creatures aside. Make sure your fans are all turned off for the night, and know that anyone experienced in dealing with temporal creatures (or well read) will probably be expecting them (even if they aren’t expecting you to use them for security). Additionally, if someone has been hired to steal from you, their employer will probably (unhappily) remind the thief of their task.
5. Observation Orbs
System Security Level: 2/5
System Description: No one will dare steal from you with these eyes in the sky! No need to conjure eyes into the back of your head when you can simply place our Observation Orbs wherever your blind spots may be!
How it Works: A system of small crystal orbs connect via scrying magic to a central viewing orb. Due to the modular nature of this system orbs can be added, removed, and placed wherever is most beneficial to insure total coverage of your shop. With the ability to store what the orbs observe for up to a tenday, the central orb can be located up to a kilometer away from the orb system. It is also possible to chain the orbs together, and even add additional viewing orbs to the system for surveillance from multiple locations.
System Secret: Spells or items that prevent scrying will prevent someone from appearing on the orbs, and they are unable to see invisible creatures. They are also easily obscured, so a fog cloud spell or such could be used to obfuscate a thieves intentions.
6. Floating Security Jellyfish
System Security Level: 3/5
System Description: Don’t. Touch. Anything. Floating, translucent, glowing jellyfish surround the inside perimeter of the shop. When on guard, their tentacles shoot out, still attached to their body, but fully extending in each direction.
How it Works: Floating, translucent, glowing jellyfish surround the inside perimeter of the shop. When on guard, their tentacles shoot out, still attached to their body, but fully extending in each direction. When moving, their tentacles float behind them, as if they were swimming through the ocean water. As soon as a character walks through the door around 2-3 jellyfish float around the person and follow them. If the person steals something, the jellyfish follow them out the door and touch them with their tentacles. As soon as the person is touched, they turn to stone. At that time the shopkeeper calls the guards and has the person taken to jail. After 8 hours the effect wears off, typically while the person is in jail.
System Secret: Jellyfish are obsessive. Each group obsesses over one scent: it could be something like the smell of fresh, sweet mushrooms, grave dirt, rose cologne, or wet leather. Whenever the jellyfish smell the scent of the GM’s choosing, they all swarm whatever carries that scent, leaving the shop items unattended.
7. Antimagic Field across entrance 
System Security Level: 4/5
System Description: Trouble with halflings wearing rings of invisibility? Been ripped off one too many times by kids from the mage’s conservatory wearing an invisibility cloak? Or maybe you sold a couple potions of gaseous form only to have your store robbed that night by what witnesses described as a puff of mist? Worry no more! Just install Mort’s Magical Antimagic Field and laugh as these mischievous magical marauders are caught red handed!
How it Works: permanent antimagic field across the entrance so any visitor must pass through it. Removes any temporary transmutations, dispels magical disguises, disrupts wards and countermeasures against detection. The interior is hallowed, using the Extradimensional Interference effect, so nobody can bypass the entrance via teleportation.
System Secret: Sadly, the antimagic field is itself susceptible to an antimagic or dispel magic spell. Additionally, it provides no protection whatsoever from mundane means of malarkey.
Tip: You can hint at the security system by having characters notice a tingle as they pass through the entrance. And of course it will end or suppress any magical effect on them. This can be a lot of fun if someone has disguised themselves through magical means.
8. Wizard Security Guard
System Security Level: 2/5
System Description: Is your nibbling a mage in training and trying to pay their tuition? Or maybe you know a magical person who needs some extra cash for spell components? Why not hire them on to keep tabs on your customers!
How it Works: Anyone entering is scanned by a 1st-level wizard whose job is to stand there ritual-casting detect magic over and over all day long. The wizard notifies bank staff if there are any suspicious magical auras on you or the items you offer for trade.
System Secret: Since the wizard is only level 1, they’re incredibly weak, and could be killed quite easily. Good help is hard to find!
9. Deal with the Dragon
System Security Level: 5/5
System Description: They’ve put together an expert team. One last heist and they can all retire. This is the big one. The plan is perfect. They infiltrate the bank without any hitches. The security expert cracks the code and they enter the vault… Only to find an ancient gold dragon who is NOT interested in parting with their hoard! The next morning you come into the bank and find a dragon who is happily picking their teeth with the charred femur of the renowned and now (permanently) retired bank robber.
How it Works: First, you must convince a dragon to help you. Truly the best way to do this would be to steal a dragon egg and raise one yourself, but that comes with some complications of its own. However, there are few things in the multiverse that dragons love as much as their hoards, and your next best bet is to convince a dragon that adding their hoard to your stash/vault is in their best interest (and the best way for them to earn some interest!) If you can keep them well fed, and continue to add to the pile, getting a dragon to exchange their cave for your vault should be no trouble at all!
System Secret: While protecting the reserves of your operation would be quite easy, you may find it difficult to make a withdrawal. On top of that you must always be wary of Wizards hiring halfling burglars on the behalf of dwarves seeking to reclaim lost glory, or of those whose knowledge of dragonkind and their desires surpasses yours.
Tip: Perhaps there is something this dragon desires and craves more than anything else, including their hoard. This could be power, a certain item, a lost love… What was a heist can easily become a campaign if the dragon is willing to negotiate.