What is the word that describes all the devices that express time?
noun: chronometer; plural noun: chronometers
an instrument for measuring time, especially one designed to keep accurate time in spite of motion or variations in temperature, humidity, and air pressure
I believe this is the largest category that encompasses every possible device whose function is to measure the passing of time.
"Timepiece" is the one that probably best describes the familiar kinds of time-keeping devices that a layperson is likely to encounter. And, to JamesK's point, there really is a staggering diversity of sub-species; in very many contexts, a more-precise term is better.
"Chronometer" is also what people call expensive watches. But, the expensive watch market is driven by a relatively small group of fabulously rich people who have more money than anyone could possibly spend in a lifetime, and we should not let their peacocking co-opt this term.
More usefully, anybody whose life literally depends on accurate timekeeping (e.g. divers and astronauts, who have to ration breathable atmosphere), will insist on a "chronometer," but those don't need to cost $100,000 (yes, really).
There are words (gotube gives "timepiece") but these are relatively rare and technical. I suspect that in your language the distinction isn't usually made, and you are want to translate a sentence that uses this ambiguity from your language to English.
But if you write "I'm going to get my daughter a timepiece for her birthday." It will be very odd, even if it is the literal translation. "Timepiece" is technical and rather dated. It is used by people who insist that a "clock" must have a "bell" (see the etymology for why). If you want to write in natural sounding English, either choose "watch" or choose "clock", or write "watch or clock" (and perhaps rephrase).
I'm going to get my daughter a clock for her birthday, or perhaps a watch.
So this is my point. In English, watches, clocks, sundials and hourglasses are all "different", but "wallclocks" and "mantelpiece clocks" are types of clock. Wristwatch and pocket watch are types of watch. In other languages perhaps "watches" and "mantlepiece clocks" are the same, but wall clocks and sundials are different. Or "hourglasses" and "sundials" are the same, but watches are different... etc.
A "timepiece" is relatively technical term for sundials, clocks, watches: any device that lets you know the time. A clock is a large timepiece that may be hung on the wall, or stand on the floor or on a shelf. A watch is small timepiece that fits in a pocket or on a wrist. Clocks don't need to have chimes (even though their name comes from the Latin for "bell") and watches don't need to have alarms (despite the etymology). Timepieces can have bells or alarms, although the word is sometimes used by people who limit the word "clock" to "timepiece with a bell".
So, my advice: Use either "watch" or "clock" as appropriate.
And note that most young people actually don't use watches, they use their phone to tell the time.