Home-brew spell effect 'Scout ward'

[TrustNo1]

I am running a home brew campaign that I am modeling after the old scifi show Stargate. The PCs will open a portal to a random dungeon that I have created. The portal will only remain open for a set amount of time, so that i can put a limit on their resources, before the PCs are violently ejected back to their original plane. I wanted to make some sort of magical scouting device that the PCs can use to see what is on the other side of the portal. Sort of like the robotic device that was used in the early episodes of the TV show, but more magical rather than robotic. I envision combining spells effects like scry and mage-hand and giving it a range. I am thinking that the scout, a floating eyeball, would have no attacks and would be destroyed if attacked at all. I want it to pass through walls at a significant cost to its range based on the thickness of the wall and the material it is made of. I was also thinking of giving it the ability to go invisible, at a significant cost to range. Can you guys give me some advice or give a perspective that I haven't thought of before I introduce this to my players? Thanks in advance, and stay safe out there.

[Smallfoot]

So it's kind of a cross between Arcane Eye and Questing Stone, with some enhancements. Ok.

What do you want the players to be able to accomplish? What do you want to prevent them from doing? Knowing what you're going to encounter makes a huge difference in whether an encounter is significant or trivial, so how will you adjust encounters if they don't spot the things you expect them to, or the reverse? Will the players be able to stack any kind of perception on top of what the Scout can do, such as adding a See Invisibility?

[Quixote]

Why not just use the spell Arcane Eye to get started? Making it visible and fragile will make the effect significantly less potent, so you could add in some extra stuff as needed.
Maybe a little homonculus with one big eye for a head or an eye-fly or -spider or -cat or -worm?

[Firebug]

Insect Scouts would at least get them the floor layout and some rerolls against traps/stealth. Spell level 2-4 depending on class.
Prying Eyes gets you better scouting, since it can report on creatures, but still doesn't allow passing through walls. Decent Stealth, but not invisible. Spell level 5.
Spectral Scout gets you incorporeal to go through walls but... its dumb. Animal level intelligence so lots of hand-holding. Pick a stealth animal and it should be decent for scouting. Spell level 3.
Arcane Eye has the problem of "The eye can't enter another plane of existence, even through a gate or similar magical portal." Spell level 4.
Questing Stone is just an Arcane Eye that can pass through Gates/Portals(but you lose contact while on a different plane), and has to be targeted on an Ioun Stone. Also spell level 4.
Share Senses could work, if someone had a suitably incorporeal familiar. Say an NPC that has Transfer Familiar and maybe Duplicate Familiar Spell level 3-4.
Traveling Dream is basically an Arcane Eye with extra flavor, still can't cross planes. Spell level 4.
Vicarious View could work, but you would still need the incorporeal scout. Also much shorter duration than most of the others. Spell level 4.
Commune with Plane could get you most of what you are looking for. Just no actual object/creature doing the scouting. Maybe reflavor the 10 minute casting time as the scouts doing the scouting. Might have to tailor the spell to always return "the layout and topography of local terrain", "presence of creatures native to the plane" and "presence of powerful nonnative creatures". Doesn't seem like it gets traps though. Spell level 5.

Depending on party level, I would probably go for Insect Scouts at low level and Commune with Plane at higher levels. Or both. It really depends on how much information you want to give the party.