What the Night Watchman's Clock Could and Couldn't Prove

A commenter on a British museum’s page for a 1950s watchclock remembers a colleague from the 1980s who took every key off its hook on his first round of the night, using a screwdriver. Then he sat in the security office and turned each key at a plausible hour, returning them to their hooks before the last tour. The commenter put a smiley after the story. The record, meanwhile, would have shown a diligent guard.

That anecdote answers the question people usually ask about these devices. Guard tour systems verify rounds by making each checkpoint leave a mark that is hard to forge, such as a numbered key at a fixed spot that prints its number on a paper record locked inside a clock. What the mark proves is that someone turned that key at that time. Whether a person was awake, walking, or looking at anything is a separate claim the paper never made.

How the clock worked

A watchclock was a mechanical clock, about five pounds by one description, carried on a shoulder strap. Keys, each cut with a different shape, hung on chains at points along the route. The guard turned the key in the clock, and the clock stamped that key’s number onto a disc or tape that already had the hours printed on it. Discs ran about 24 hours; tapes could run up to 96. A supervisor opened the clock the next morning and read the record.

Printing the times in advance was the central design choice. A guard could not write in a convenient hour, because the paper already held all of them. The only variable the guard controlled was which key got turned when.

The idea is older than the famous brands. The Victoria and Albert Museum holds a night watchman’s clock by John Whitehurst of Derby dated 1806. The gallery label says it was used at Etruria, the Wedgwood works, and that the watchman pressed a lever to push pins on a dial while the foreman checked which had moved. The case was locked and the pins reset themselves after 12 hours. Etruria is the same factory world as the mill bells and fines Thompson wrote about, and the logic is the same: the owner wanted a witness that did not sleep.

The cheating was anticipated before the cheating was recorded

I could not find a trade-journal or labor-history account of specific frauds from the nineteenth century. What survives is the patent literature, which reads as a list of worries.

A Scientific American item of 25 December 1852 describes a “Watchmen’s Register Attachment” by P. M. Statzell and J. L. Kucker of Philadelphia. It says the chief drawback of existing instruments was their “liability to be tampered with by an unfaithful officer.” The fix was a ratchet that would not let the watchman advance the dial more than one step at a time, which implies the trick it targeted: skip a visit, then wind forward to cover it.

Charles Weinedel of Louisville filed a patent in December 1892, granted in December 1893 as No. 510,745. His device was built so it “cannot be tampered with by the watchman,” had a casing the watchman could not remove, and locked out the next signal until the half hour had run. It also required the dial to match the central office’s report, to stop “watchmen and operators at the central station from working together.” So by the 1890s inventors had enumerated three cheats: tamper with the instrument, signal early, and collude with whoever reads the record.

Detex, the successor to the Newman Clock Company, answered one more. On its clocks, every opening or closing of the case punched a hole in the disc at that moment, and a disc with more than two perforations showed the clock had been opened. The clock could not stop a guard from opening it. It could make the opening visible to the person reading the paper. The anecdote above shows the limit: a guard who turns keys in the office never opens the clock at all.

One more weakness was social, not mechanical. A contributor to the same museum page, Phil Davies, wrote that a fixed numbered route let anyone watching learn where the guard would be and when. He says that once he varied his patrol order, break-ins fell by more than 90 percent. That is one person’s memory on a comments page, and I would not generalize it.

What the record proved, and what it left open

Put the evidence together and a watchclock verified three things reasonably well: the key was turned, at a time the clock believed, in a clock that had probably not been opened. It verified nothing about the person. A guard could be drunk, asleep between keys, or absent for the middle of the night and still produce a clean disc, as long as the keys got turned.

This is the general problem with proof of presence. The proof attaches to an object or a place, and presence is what you wanted. Every later system, from punch cards to badge readers, repeats the gap in a new form. Employers who tried to close it with fingerprints discovered a different set of costs, in Illinois courts.

Detex stopped making mechanical watchclocks on 31 December 2011. It had made the Newman for about 130 years, though company histories date the Newman Clock Company to the 1870s, so I treat the figure as approximate. Familiar claims that the first watchclock came from a German named Imhaeuser in the 1850s did not hold up when I checked: the patents I found under that name are from the late 1870s, and a collectors’ site says the origin of the style is uncertain. I have left the date out.

Where a video check sits

Compare this to a wake-up. A watchclock-style check on an alarm would be a button you press, and a button proves a thumb. A video proves more, because it needs a face, a room, and a particular moment. It also has holes. Someone can film themselves upright, put the phone down, and go back to bed. Nothing in the file shows they stayed up.

An app like DontSnooze, which asks for video proof, has the same hole, and I still think it beats the clock for waking up, for one reason the clock never had: a friend is on the other end. A guard’s disc was read by a supervisor at the end of the shift, a stranger with a ledger. A friend notices that your “I’m up” video is the fourth sunrise-free kitchen shot this week, and that kind of audience closes holes that a better sensor cannot. For why self-report fails and a recording does better, see the comparison of video proof with saying you’re up.

Questions about guard tour clocks

How do guard tour systems verify that a security guard actually did their rounds?

They check that the guard visited each fixed checkpoint in a plausible order and time window. Mechanical watchclocks did this with numbered keys that stamped a paper record locked inside the clock; modern systems use scanned tags or chips and a software log. Both prove a checkpoint was touched, not that the person was alert while doing it.

How did guards cheat watchclocks?

The accounts I could verify are few. A museum commenter recalls a guard in the 1980s who took the keys off their hooks on his first round and turned them from the office later, and says the paper tape on his model could be broken. Early inventors also worried about watchmen advancing a register by several steps to cover missed visits.

Are watchclocks still made?

Not by Detex, the largest US maker, which stopped producing all mechanical watchclocks on 31 December 2011. The Newman model had been in production for about 130 years, and the company’s electronic guard tour line continued. Used clocks and keys circulate among collectors.

Can a video check be faked as easily as a guard tour?

It can be faked, but differently. A watchclock key needs no face and no timing beyond the route, so anyone can turn it, while a video needs a specific person on camera at a specific moment. The remaining gap is someone recording and going back to bed, which a human audience plausibly narrows by noticing, though I know of no study that tests it.