Right. :)
So fair warning: when I explain something I tend to give a great big brain dump of every useful thing I know about it. I'm trying to keep it as short as possible, but there is a lot to say. Most of what follows you only need to read once, and then it will stay with you forever. The section on the commands is short and you might need to refer back to those a few times, but there's some longer explanation up front.
Snitches send you messages when someone enters or leaves within an 11 block range of the jukebox. They also record block editing actions.
It helps to understand Citadel (protections) pretty well. So here's an overview.
In Citadel you can strengthen something as you build it, with /ctf (F for Fortify), or you can strengthen it after it is built with /ctr (R for Reinforce) . Either way, you use stone, iron or diamond. Stone makes something 25 times stronger (25 times as long to break), iron is 250 times and diamond is 1800 times. Diamond-Reinforced Obsidian (DRO) is the strongest block in the game and takes a single person with a high eff pick 1800 times however many seconds that takes to break normally. When people go vault raiding they go in a large group and all work on the same block(s) simultaneously.
You can protect stuff in your own name, which is simplest, but it's more hassle in the long run if you share a build with someone else because to change things over to a shared protection you have to go around and punch every single block. So I'm just gonna teach you the commands to work with groups. With a group you can easily allow people to edit blocks, use chests or other containers, open doors, and receive snitch messages. Snitches only warn about people who are not on the group that the snitch is protected by. So by adding people to the same group as the snitch, you can turn off warnings for them (that's useful because snitches tend to spam chat). You can also give people permission to moderate a group you own, which means that they can add other people. You give that permission only if you really trust their judgement about other people, depending on how important a thing you're trying to protect.
It's a good idea to have different groups for different purposes. You might have one group for the front door of your house. Another group to go through doors deeper inside. Another group to edit the walls. Another group to access the chests. And finally another group for the snitches. The reason you might want so many groups is that you trust people to do some things and not others. So you might be fine with someone coming in the front door (but of course that means they can let other people in), but you might not want them making holes in the walls and you probably don't want them rummaging through your chests.
For simplicity, you can start out with a single group for your whole house (walls, doors, chests and snitches). It's not too much trouble just to punch a few blocks (chests, doors, snitches) later to change them over to a different group. It's really inconvenient, however, if you have to change thousands of blocks for a wall, or if you have hundreds of chests. I'm going to show you how to set up a group for your front door and a separate one for your house build and snitches. That is, two groups:
orion_front_door - people who can come in the front door, but not further into the house.
orion_house - the build itself, your chests, your snitches. People you would trust to edit your house and rummage your chests unsupervised (no snitch logs). You can easily set up another group for a different level of trust on the chests later on if you find you need to.
Right now, all your protections are probably private (just you) if you protected stuff without using a group, and that's perfect for your chests right now until you find yourself wanting to share with someone else.
So first create the groups:
/ctcreate orion_front_door
/ctcreate orion_house
Now if you wanted to change something over to a different group, like for example the front door, you can use /ctallow to add someone, and /ctdisallow to remove them. And you can use /ctmembers to see who is a member (and /ctmoderators to list people who you've given moderator privileges on the group to).
So if you want to allow Norami to come in the front door and take shelter in the house, for example (names are not case-sensitive):
/ctallow orion_front_door norami
Then you can use /ctr (R for Reinforce) to change the group on the door from your private one to the new group. You type:
/ctr group orion_front_door
and then put a piece of reinforcement material (e.g. stone) in your hand and punch the doors. You may have already fortified the front door with diamond (or whatever). /ctr will not change the strength of an enforcement. If it is already diamond, it stays diamond and doesn't downgrade to stone. /ctr will change the group of an existing reinforcement though, and that's what you're doing here. If you have never reinforced the block, then /ctr will actually take the reinforcement material out of your hand when you punch blocks and store it inside the block you're protecting (e.g. a wall).
The downside of using /ctr to reinforce large builds is that after you have built something un-reinforced, you need to go back and punch every single block to protect them all. It's like building the thing twice and you may even miss a few blocks. A much better way to build things is with /ctf (Fortify). I learned this the hard way. With /ctf, you hold the reinforcement material in your hand before you type the command, then, for example to build your house:
/ctf group orion_house
Then the reinforcement material will be taken out of your inventory with every block that you place. You can turn off this reinforcement mode with /ctf again, or even switch to a different material (e.g. iron) by holding that material and typing the command again. It's a good idea to keep the fortification material (e.g. stone) in your hotbar when you are building. Then you can see them being used up as you place blocks. If you have a full stack of stone and a full stack of, say, blue stained clay blocks, then you should have the same number of each left over after you have built something.
If you put a block in the wrong place when you build, you're going to want to break the blocks you've fortified, and so you use /ctb (B for Bypass) to bypass the protection on blocks you have permission to edit. You will get back the reinforcement material when you break the block. Watch carefully though, because the material will fly away from the block. I tend to leave bypass mode on for the whole time that I am building. And you can use that command to turn bypass off again.
To check what the reinforcement of a block is, you can use /cti (I for Information) and then punch that block. And you can use that command to turn it off. If you don't have permission on a protection, /cti will tell you that something is protected, but not who owns it. None of the Citadel commands can tell you who owns what, which is good for maintaining secret bases.
To completely turn off all Citadel modes you use /cto (O for Off) and that is a good short command to use to get everything back to normal (no bypass, no fortification, no reinforcement, no information).
If you decide later on that Norami's actually an evil griffer, you can remove her from the door group without having to punch the front door:
/ctdisallow orion_front_door norami
And incidentally, if you forget any commands, /help works; you can do /help citadel to list all the options, and then something like /help ctallow, for instance.
So finally, to place your snitch: let's say that you want to put it on the same group as the house. Grab the snitch (jukebox) and a diamond to reinforce it with. You want to reinforce blocks with a material worth about the same as the block. A jukebox takes a diamond to make, so it's worth a diamond to protect. A normal piston takes 1 iron, so you'd just reinforce them with iron. But slimeballs currently cost a diamond apiece, so it would be a good idea to protect sticky pistons with a diamond each. (Incidentally, for pistons, note that they can only push unreinforced blocks.)
You want to hide your snitch, because someone with a good enchanted gold axe could steal it. If you can't hide it, you might want to enclose it in DRO, depending on how cautious you are. Find a good spot about centre of your house, hidden under the floor and 11 blocks or less from the top of the roof. And of course, no more than 11 blocks from the furthest wall. Then put a diamond in your hand and set up to fortify the block as you place it:
/ctf group orion_house
Now you can place the snitch. Now it's a good idea to give the snitch a name. Because if you have lots of snitches it's hard to work out which one is sending you messages based only on the coordinates. So when you're close to the snitch use janame to give it a name:
/janame orion_house
And then you will see that name in the snitch messages. When you are close to the snitch, you can also check the logs:
/jainfo
/jainfo 2
/jainfo 3
/jainfo 4
The number after /jainfo specifies the page to look at. Higher numbered pages are older and page 1 is always the most recent history. Snitches only keep logs for a limited time. And also be aware that a snitch will revert back into just a normal jukebox if you're not around for a couple of weeks.