I was drilling through the wall (above the radiator, but not above any pipes or sockets) and hit something metal. I have drilled a tiny hole in that metal plate. It's not copper, looks silver. What is this? Can't identify what it could be
Stop. You probably hit a metal plate protecting plumbing or wiring behind it. It's there specifically to prevent people like you from drilling through it and electrocuting yourself or causing a flood.
I recommend you stop whatever job you're doing and consult a professional, or at least a handyman.
I'm glad you noticed & didn't go further. You'll need to drill a hand width away from that area. Of course, if possible find out what it is. If you can't get a visual from an attic or basement, then you can drill a bigger viewing hole away from it to confirm there are utilities being protected by the plate. Use a depth-stop on your drill...drill a hole through a thick block of wood so just enough drill bit is protruding. You'll then need to patch both holes.
I would first like to congratulate the others for giving good possibilities, but would like to add another: You hit a stud.
Depending on the size of your drill, it might just look like a plate, but its a little piece of architecture that you don't want to hit (mostly for your drill's sake.)
I suggest filling in the hole with Spackle, then drilling elsewhere nearby, but only after checking for another stud or metal piece.
This can be accomplished with a good strong magnet (sometimes,) but also with a mid-price handheld device called a stud-checker.
All of the above responses seem to be spot-on for possibility. Building codes and then material usage in construction vary from region to region. If it is a protective metal plate (ie - a pipe for water,sewage, or electrical wiring is under this plate) it is a heavy and thick steel, and hard to accidentally punch through. (Unless you have professional type drill bits) I'm betting a steel stud.(Since you did not get a nice shower, trip a circuit breaker, or actually NEED to call a professional :) ) If you're drilling into a wall, maybe you want to hang or mount something on that wall. You would want to find that stud if your place was built with them( or remodeled with an extra wall or two...) It will grip a screw well enough to suspend your item. Use appropriate hardware to mount anything. Find out what that screw or mounting hardware(drywall anchor?) should be. Otherwise: If it took you a bit of effort to push your 'tiny' drillbit through that metal... try somewhere else on the wall. Get someone to look at it too, just in case. Better safe than sorry. Always good to ask someone who knows. Luck
You might look on the other side of the wall to see if there's something electrical that has a metal box around all except possibly the front part. For example, an electrical outlet, an electrical switch, or a circuit breaker panel.
Also, check for a heating/air conditioning vent, both on the other side and from above and below. Those use thinner metal than is used for electrical equipment.
Thank you all!
Think it's the alluminium stud - there are no electrical outlets or pipes anywhere around. It's an internal plasterboard wall. There is nothing on the otherside - just another room (no electrical outlets on that side either). Plus the depth of the new hole is only about 1 cm, logic suggests wires & pipes should be burried deeper than that. The drill bit I was using is for wood, not metal. So I don't think I would have been able to drill a tiny hole with it through a metal plate!