Weathervanes are a cute way to make your home look just a little different, and a little characterful. A weather vane is a simple device, usually made from light metals either cast or welded together, that points in the direction of the wind. It then also features an arrow pointing to the north, so you can easily read the direction the weathervane is pointing. It accomplishes this by mounting part of the device on an axle on which it can easily turn, and this part is then weighted such that it will turn to face the wind. That part of the weathervane is traditionally shaped like a rooster, but you can find weathervanes in all sorts of designs, such as bears, cats and more. The rooster really isn't in any way a functional part of the weathervane, and weathervanes that are part of modern day meteorological kits don't have any. Weathervanes were invented in ancient China and Greece more or less at the same time in the second century BCE. These days, weathervanes have lost a lot of their usefulness with modern meteorological technology though, but there is still a lot of charm to having a old-fashioned weathervane mounted on your roof, or on some other elevated feature on your property.
If you're interested in seeing the effects of changing weather for yourself in a measurable way, you can get a different product as well, called a rain gauge. A rain gauge at its simplest is a flask with millimetre measurements written on the side that you mount somewhere in your garden, usually on a stick that is provided with the rain gauge, or on your fence. There are also rain gauges that have been made to look like attractive garden features on their own.
But when it's not raining, sundials are another different product featuring somewhat obsolete bit of old-timey technology that is nonetheless charming and can make for a great garden feature in the right place. Sundials, more so even than weathervanes, come in a huge variety of styles that you can use to either establish or match an aesthetic for your garden.