A carriage clock is typified by five bevelled-glass panels set in a brass-framed case displaying a polished brass movement inside and topped with a handle. First, never trust the handle to lift a carriage clock without cradling it underneath in the other hand for support. I've never seen a handle come off but they are only fixed with a short pin and it's just not worth the risk; the consequences could be terminal.
Many carriage clocks had red leather cases to protect them, with a removable panel on the front so that you could still see the time. Some had alarms to wake you in the morning. Some strike the hours and some have a button to repeat the last hour, or even quarter hour, so you did not need to light a candle to tell the time at night.
There's no pendulum - carriage clocks were packed with your other luggage while travelling (in your carriage) so they needed to work whether standing on the bedside table or lying on their side. Some English made carriage clocks had a type of pocket watch movement fitted but the majority you'll see are French and have a flat platform on top set with an escapement visible through the top glass. It's like the one in old mechanical watches but bigger; a wheel on a hairspring rotating back and forth five times a second. It might have a lever escapement or a cylinder escapement; they look quite similar but the cylinder type has a plain three-spoke balance wheel whilst the lever type tends to have six or eight balance screws on the edge of the wheel and is better.
The very first carriage clocks appeared in around 1830 and had one-piece cases, the parts fused together. Gradually these gave way to multi-piece cases, which were much cheaper to produce in quantity. Multi-part cases were so called because they are made by assembling pre-formed parts that had been hand finished. Most parts have two or three digits stamped on them to help the assemblers identify which parts go together. The vast majority were made in France in towns around Paris; but beware the elaborate Chinese imports that are brand new but sometimes deliberately aged to deceive Read more about fake Chinese carriage clocks to avoid.
Carriage clock case style varies a great deal but the commonest are the plain 0bis, which has a flat top, and the Corniche, which has a raised and slightly more decorative top but is otherwise much the same. Both were popular from 1880 until 1930 and were mass-produced for export to the UK and US. You will often see Made in France (in English) stamped on the back after 1900. Some of the better makers of carriage clocks include Margaine, Garnier and L'Epée but Maurice & Cie are often overlooked. Factories like Japy Frères, Leroy, Douverdrey and Bloquel, and Richard & Co, turned out thousands and thousands of carriage clock 'blancs' every year for other makers as well as retailers like Tiffany, Garrard, and Mappin and Webb.
Keys for carriage clocks are typically double ended, one for winding the eight-day movement (counter-clockwise) and the other for making adjustments to the hands from the back as the dial isn't accessible from the front.
There are only two really good books on carriage clocks, one by Charles Allix (I have a spare copy at £50) and the other by Derek Roberts. They are lavishly illustrated but both long out of print so expect to pay at least £60/£80 or more at a decent book dealer if you can find a copy. Otherwise, try your local library. If you can make do with fewer pictures, Laurie Penman produces the best of those currently in print.
My flat rate for overhauling a carriage clock timepiece is £150 and for a striking version it's £200. For more complex versions like repeaters, quarter chiming, grand sonnerie, I will need to see it first but it will not be less that £225. For that, I'll strip the movement, clean it, check it for wear and proper alignment and engagement of wheels and pinions, rebush up to two worn pivot holes, and set it up correctly. These prices include stripping and cleaning the escapement platform as well, which is essential. As the movement is visible, you might want it polished (£35/£50). And any work on the case will all be additional depending on what's required.