is there a D&D equivalent of a transmitter/bug?

[King of Nowhere]

I envisioned a plot where the party is tracked by hiding a small object on them, the magic equivalent of a gps localizer, possibly with some other functions similar to modern spying equipment.
Now, while I have no problems homebrewing that stuff, I wonder if they actually made one in some splatbooks.

[MisterKaws]

From memory, I can immediately recall Trail of Haze, but I know there's a few Ranger-only spells that do the same, and some PrCs can also do something similar.

Also Metafaculty can skip through the need of a GPS.

[Mike Miller]

I envisioned a plot where the party is tracked by hiding a small object on them, the magic equivalent of a gps localizer, possibly with some other functions similar to modern spying equipment.
Now, while I have no problems homebrewing that stuff, I wonder if they actually made one in some splatbooks.

So you want a continuous scrying effect? It sounds like something that should exist. Nothing specific comes to mind though. I feel like this is Dragon magazine territory.

[Biggus]

Doesn't act as a GPS, but the Bard spell Listening Coin (SpC) allows you to 'bug' people unobtrusively.

The Cleric spell Status (PHB) enables you to know the distance and direction to a touched creature. It's intended for use on allies, but doesn't say "willing creatures only". Cast stilled and silenced it could be used as a GPS when you "accidentally" touch someone.

Both last 1hr/ level and have no range limit.

[Psyren]

Put your psicrystal in their bag - 1 mile telepathic link with the owner and can report back everything it hears/sees. Even if they find it, it's just a funky rock.

If you're worried about getting it back, slip a soul crystal of psionic teleport in there with it that it can use to escape back to you.

[Techwarrior]

Locate Object should do what you want. A custom continuous magic item that only detects where the other half of the magic item, that you then plant on the trackee should do the trick.

[MisterKaws]

Put your psicrystal in their bag - 1 mile telepathic link with the owner and can report back everything it hears/sees. Even if they find it, it's just a funky rock.

If you're worried about getting it back, slip a soul crystal of psionic teleport in there with it that it can use to escape back to you.

Persistent Polymorph one Dvati twin into a Hoard Scarab and send it into their bag of gold. Full tracking anywhere in the multiverse, though it needs to be re-cast daily, and would be identifiable with Arcane Eye.

Alternatively, cast Curse of Lycanthropy to turn the Dvati twins into Were-Hoard Scarabs. Would fix the magic aura issue.

[Zaq]

I thought there was something (a spell, probably?) that let you know the location of an object bearing your arcane mark, but that may have been homebrew. Maybe Eberron, though? Feels relevant for House Kundarak or House Sivis.

I also have a vague memory of there being a PrC ability or two, probably in ranger-ish PrCs, of being able to unerringly track down specific targets, but I don’t think they were subtle. Going from memory, though, so I might be way off base.

[Palanan]

Originally Posted by Zaq
I thought there was something (a spell, probably?) that let you know the location of an object bearing your arcane mark, but that may have been homebrew.

I could’ve sworn I’ve seen something like this too.

Originally Posted by Zaq
I also have a vague memory of there being a PrC ability or two, probably in ranger-ish PrCs, of being able to unerringly track down specific targets….

You might be thinking of the Bloodhound from Masters of the Wild, which has some trackey abilities. Not sure if they’re unerring, but there are some bonuses and SLAs along that general theme.

[MisterKaws]

I thought there was something (a spell, probably?) that let you know the location of an object bearing your arcane mark, but that may have been homebrew. Maybe Eberron, though? Feels relevant for House Kundarak or House Sivis.

I also have a vague memory of there being a PrC ability or two, probably in ranger-ish PrCs, of being able to unerringly track down specific targets, but I don’t think they were subtle. Going from memory, though, so I might be way off base.

Dragon Magic: Dragoneye Rune.

We done it boys. Girls too :P

[Bohandas]

Listening Coin Spell Compendium pg.133

[Efrate]

Can't a cancer do something similar with cysts they place in people or am confusing some house ruled stuff for a bbeg back in the day?

[Segev]

Can't a cancer do something similar with cysts they place in people or am confusing some house ruled stuff for a bbeg back in the day?

Necrotic Cyst is a 2nd level spell in Libris Mortis. It makes the target vulnerable to a line of Necrotic spells. The other second level one is Necrotic Scrying. Cast it targeting any creature either a Necrotic Cyst, and you can scry them out.

Necrotic Spells require you to take the Mother Cyst feat, also from a Libris Mortis.

[Braininthejar2]

There was a magic item that looked like a beholder statue / knife stand

Each stalk was a dagger, that could be removed and given to people, and the owner of the head could later touch it to see through the pommel gems.

[Darrin]

Doesn't act as a GPS, but the Bard spell Listening Coin (SpC) allows you to 'bug' people unobtrusively.

There's a similar spell called spymaster's coin in Complete Scoundrel. Similar duration, but the spymaster version has the option to give you visual information instead of audio.

[AnimeTheCat]

Discern Location can be used in conjunction with a token, coin, or other object previously touched by the caster. My suggestion would have it be a slip of paper or something that is stitched inside of an article of clothing or similar that the individual you're trying to track will alway have or wear. It doesn't even have to be magical, which means detect magic, arcane eye, etc. won't protect you and if you're unaware of it in the first place you're practically defenseless against it since there is no save for the object.

[jintoya]

Discern Location can be used in conjunction with a token, coin, or other object previously touched by the caster. My suggestion would have it be a slip of paper or something that is stitched inside of an article of clothing or similar that the individual you're trying to track will alway have or wear. It doesn't even have to be magical, which means detect magic, arcane eye, etc. won't protect you and if you're unaware of it in the first place you're practically defenseless against it since there is no save for the object.

This on a bit of fabric, affixed to the underside of the soul of the shoe as they sleep, alternatively you could just use the shoe itself.

Also, if you wanted to... Just have an item like a crystal ball that can be used to cast a continual scrying spell, you could have him shatter it if they discovered it, or it explodes of it ever sees itself (just feedback loop as explanation)

There was a warlock invocation that makes the warlock appear mundane no matter what he's doing, I can't remember if it mimics a spell, but using that on an item would have them ignoring it on a failed save.
It would be like "rations, gems, coin pouch, scrying stone, extra lantern oil... Nothing strange in here!"
(It might be from a thread on the forum even, hard to remember because I have allot of warlock invocations, after a while you forget what's custom)

Edit:
A phylactery cannot be located, need only be of MasterCraft quality and a lich with one always knows exactly where it is, but nobody else can detect it's properties.
Who says it has to be a lich?
Why can't Carl the whight get one?
Now Carl is the BBEG's compass, good job Carl!