I have a 7th-level wizard NPC who would like to be secretly alerted if someone enters an underground location that is important to him. He will always be within 20 miles of the location. He would like to set up this "alert" once and then have it last until triggered; he would not want to have to return to the location to re-cast any spells very frequently. (Returning once a year or so would be OK.) Ideally, the intruder would not be aware that anyone is monitoring this location. The wizard has a normal amount of resources, so no solutions which cost zillions in gold. Is there a way to do this, without homebrewed spells/items?
Ideas I have considered (and rejected, with reasons):
- alarm. Problems: only lasts 8 hours. Also the mental "ping" has a range of only 1 mile, but the duration is the dealbreaker here, otherwise it'd be perfect.
- Cast glyph of warding with a trigger of "someone enters the location". Cast skywrite [EEPC] into the glyph, to write "Intruder!" or similar into the sky when the glyph is triggered. Problems: the location is underground and so the sky can't be seen from it, and skywrite requires the caster to be able to see the sky. Also has the problem that other people can see the "alert" in the sky, although what's written could be made obscure to make this less likely. It's also not all that efficient; our wizard has to look at the sky pretty regularly (how often do you look at the sky?)
- A magic mouth "telephone wire" (discussed at GitP). Basically, you cast a chain of magic mouths every 30ft between the location and the wizard, where the first one is triggered by an intruder and whispers "Intruder!", and all the others are triggered by the previous magic mouth in the chain whispering "Intruder!" and then say "Intruder!" themselves. Problems: costs a lot of money (10gp per mouth), and it only works to a fixed location; the wizard has to remain at the end of the (static) chain forever. It's also possible that other people may hear the chain speaking, and the intruder themselves may also hear it and thus be alerted that their intrusion has been detected.
- Create a keycharm [E: RFTLW]. Cast glyph of warding, with condition "an intruder enters the area" and tie it to the keycharm. Cast alarm into the glyph, tying it to the keycharm. If an intruder enters and avoids the glyph, that will trigger the keycharm; if the intruder does not avoid the glyph, then the glyph will cast alarm, the intruder will trip the alarm, and that will trigger the keycharm. Problems: you need to be or have the help of a dwarf with the Mark of Warding from Eberron.
- Station your familiar at the location, and have the warlock eldritch invocation voice of the chain master so the familiar can tell you about an intruder from any distance. Problems: you need to be a third-level Pact of the Chain warlock with voice of the chain master, and then give up your familiar to have it guard the location, which is a pretty heavy cost to pay.
- Find a friendly awakened shrub, or create one with a pot of awakening [XGTE] (the awaken spell is too high level). Obtain a pair of sending stones [DMG]. Since the shrub is friendly, and has human-level intelligence (10), it should be able to obey commands, and since it's a living thing that can take actions, it should be able to use an action to activate the sending stone. The shrub is defined as knowing "one language known by its creator", but it's not clear whether it merely understands that language or can actually speak. If it can speak, it can warn the wizard by sending through the sending stone. If it can't speak, then request it to use its action when it spots an intruder to activate the sending stone and then wave in the air; put a magic mouth on its pot with trigger "when the plant waves, say 'Intruder!'", and then hopefully the magic mouth can be heard through the sending. (Problems: This second approach is rather more dubious! It's not at all clear that one creature can cast sending and then have someone else do the speaking. And it's quite likely that the shrub can't speak and thus can't send anything through the sending spell, even if it can use an action to trigger the sending stone. However, the awaken spell does gift the shrub the ability to speak ("The target also gains the ability to speak one language you know"), so presumably the pot of awakening does as well.)
- Have a magic mouth trigger on an intruder and use a sending stone. Problems: I'd rule against this as a DM; the stones require an action to trigger, and magic mouths can't take actions.
- Cast contingency, with trigger "an intruder enters the location", and have it do something to you, wherever you are. Prestidigitation to make sparks appear in front of your eyes briefly, say, to warn you of an intruder. This is the perfect solution but it's a 6th-level spell and thus unavailable to our 7th-level wizard.
- Rube Goldberg approaches which involve a glyph of warding (somehow) destroying one of a pair of sending stones, thus rendering the other one (in the wizard's possession) instantly nonmagical. Problems: I don't think there's a way to be alerted that a stone in one's pocket has suddenly become nonmagical, plus ideally one would not destroy a magical item just to make this alarm work.
There are obviously homebrew or unlikely approaches (find or buy a scroll of contingency, or craft a dedicated magical item to do this), but I'm trying to find an approach without crafting a homebrew item to basically cast permanent alarm (since that's basically DM fiat in allowing it, and I prefer to have my NPCs not just pull powers out of their hats but instead follow the same rules as the PCs, when possible.) I will of course do this if necessary, but I'm hoping there's a more creative way.
A similar question was addressed at How can I set up a long-range alarm for my fortress? but this example is more constrained; the wizard here will remain closer to the location, and is lower-level (and therefore is happy to accept more constraints on the solution). But "tell me if someone enters this area, even if I'm some distance away" does not seem too outlandish a thing for a 7th-level wizard to be able to creatively do.