According to a passage in the Shiji by Sima Qian, the tomb of Qin Shi Huang (the "First Emperor" of China) is said to have contained crossbow-based booby traps designed to ward off any would-be graverobbers. The following translation is by William Nienhauser with the relevant sentences in bold:

After [the First Emperor] had united the world, more than 700,000 convict laborers from the world were sent there. They dug through three [strata of] springs, poured in liquid bronze, and secured the sarcophagus. [Terra-cotta] houses, officials, unusual and valuable things were moved in to fill it. [It was] ordered that artisans should make crossbows triggered by mechanisms. Anyone passing before them would be shot immediately. They used mercury to create rivers, the Jiang, the He, and the great seas, wherein the mercury was circulated mechanically. On the ceiling were celestial bodies and on the ground geographical features. The candles were made of oil of dugong, which was not supposed to burn out for a long time.

The tomb of Qin Shi Huang is still extant but has not been excavated yet due to concerns regarding the adequacy of current preservation techniques. This hesitance is not unwarranted; the vibrant painted colors of the nearby Terracotta Army faded away after being exposed to air. So without the opportunity to peer into the tomb for the foreseeable future, how trustworthy is Sima Qian's account? There is evidence pointing towards its validity. While rivers of mercury might sound outlandish, a study in the 1980s found higher-than-expected levels of mercury detected in the soil situated in the proximity of the tomb. This finding is further backed by two additional surveys carried out in 2003, which again found elevated levels of mercury in the soil. The mercury was also unevenly distributed, which lends some credence to the idea that that the placement of mercury might have originally corresponded to the waterbodies of China. Duan Qingbo, the archaeologist leading the excavation of the Qin Shi Huang mausoleum, writes that

Once again, these surveys confirmed that there is a large amount of mercury to be found inside the tomb. Moreover, the distribution of mercury level corresponds to the location of waterways in the Qin empire - there is no unusual amount of mercury in the northwest corner of the tomb, while the mercury level is highest in the north-east and second highest in the south.

But let's assume that Sima Qian is correct and there are booby traps lying in wait somewhere in Qin Shi Huang's tomb. So in what state would a future archaeologist find these crossbow traps? The excavation of crossbows in the Terracotta Army pits gives us an idea of what might be there. Over two hundred bronze crossbow triggers have been uncovered so far. The triggers are all that remain because any components made of wood or bamboo would have deteriorated long ago. So even if there were booby traps in Qin Shi Huang's tomb, they certainly won't be in working condition like how they are portrayed in popular culture.

A more interesting finding from analyzing these bronze triggers is that they reveal quite a lot about the administrative and manufacturing capacities of the Qin state. By analyzing the variations between bronze trigger parts (each trigger consisted of five separate parts), a study by Li et al. found that trigger parts clustered in identifiable subgroups. Furthermore, only certain combinations of different parts (eight out of a possible 48) were likely to appear for the assembly of a completed trigger. Their results suggest that the crossbows were crafted in production cells working in parallel, where each cell individually handles the manufacturing of smaller components and their assembly into a final product. By comparison, in a Ford-like assembly line model, each component is produced by a group dedicated to the manufacturing of that particular component. Martinón-Torres et al. has likened this ancient cellular production model to the lean production systems of Toyota that were pioneered in the 20th century. It's surprisingly sophisticated for the 3rd century BCE!

Li, X. J. et al. Crossbows and imperial craft organisation: the bronze triggers of China’s Terracotta Army. Antiquity 88, 126–140 (2014)

Martinón-Torres, M. et al. Forty thousand arms for a single emperor: from chemical data to labor organization in the production of bronze arrows for the Terracotta Army. J. Arch. Method and Theory 21, 534–562 (2014).

Duan, Q. Scientific Studies of the High Level of Mercury in Qin Shihuangdi's Tomb, in The First Emperor: China's Terracotta Army, pp. 204-207 (British Museum Press, London, 2017)

Sima Qian. Shiji, Nienhauser, William H. Jr., trans., The Grand Scribe's Records (Indiana University Press, Bloomington & Indianapolis, 1994) via Shi, J. Incorporating all for one: The first emperor's tomb mound. Early China 37, 359-391 (2014)