Elliott (1955/1990) describes a curious glass bottle used in the worship of Sun Wukong in Singapore. Filled with “twelve o’clock water” and topped with a consecrated bulbous glass stem, it is said to make a pinging noise to signal the arrival of the monkey god in a home or temple:
There are, also, sometimes other pieces of apparatus, apart from images, which devotees like to keep in their own homes. An outstanding example is an article of equipment almost exclusively associated with the ‘Great Saint’ [大聖] which goes by the onomatopoeic name of ‘ping-pong’ [乒乓]. It consists of an ordinary bottle filled with ‘twelve o’clock water’, water drawn from a tap or well at midday. Into the neck is fitted a funnel-like piece of glass-ware open at the lower end of the funnel, which dips into the water but completely closes the top [fig. 1 and 2]. Everyday at noon, and sometimes at other hours as well, this apparatus gives off a sudden ‘pinging’ sound, as if bubbles were rising and forcing up the funnel in the bottle’s neck. When this occurs, the shen [神, god] is supposed to be revealing his presence in the temple or the home, and an immediate act of worship must be carried out by the persons there. These ‘ping-pong’ are invariably found in temples associated with the ‘Great Saint’. Devotees will purchase their own funnels and bring them to the temple for the dang-ki [童乩, spirit-medium] to consecrate them with a lick of his blood (p. 58).
Fig. 1 – The ping-pong bottle, a.k.a. “Great Sage bottle” (Dasheng ping, 大聖瓶), fitted with the bulbous stem, which is closed at the top and open at the bottom (larger version). Fig. 2 – A detail of the stem (larger version). Images found on google.
The device was also used in Hong Kong according to one personal account shared with me:
I believe the apparatus was used not just in Singapore. My mom told me that as a kid in HK in the 1940s/50s, her aunt also had something similar on the altar where she worshipped the [Great] Saint. And when the apparatus made a noise which signified his arrival, they would light up a joss stick.
I don’t know when the bottle was first associated with Sun Wukong, but the above information points to its active use in Asia as far back as the 1950s. It’s my understanding that the bottle is a rarity in modern practice, suggesting it flourished prior to mid-century.
Why the bottle was associated with the Great Sage is also a mystery to me. But the significance of twelve o’clock water may provide some clues. Astrological theory associates noon with wu (午), the seventh of twelve earthly branches, which is in turn identified with horses, the heart, fire yang, the summer solstice, and the direction south (Wu & Taylor, 2014, pp. 133-134). Readers may remember that Sun Wukong is appointed the keeper of the heavenly horses (bimawen, 弼馬溫) in chapter four of Journey to the West (Wu & Yu, 2012, pp. 148-149). Additionally, Chinese philosophy considers the heart to be the seat of the mind (xin, 心; alternatively translated “heart-mind”). This is important as Sun is called the “Mind Monkey” (xinyuan, 心猿; alternatively translated “Mind Ape”), which is a Buddho-Daoist concept denoting the disquieted, transient thoughts that keep man trapped in Samsara. Examples include the titles for chapters seven (“From the Eight Trigrams Brazier the Great Sage escapes; Beneath the Five Phases Mountain, Mind Monkey is still”) and fourteen (“Mind Monkey returns to the Right; The Six Robbers vanish from sight”).
(Before I continue, I must warn that using the 16th-century novel as a source for modern folk religion surely overlooks beliefs that I am not aware of. The above info should therefore be considered purely speculative.)
A naturalistic explanation for the pinging noise is air escaping from the bottle due to changes in atmospheric pressure. However, I’d like to speculate on a possible esoteric reason. As mentioned above, noon is identified with fire yang, which is considered the height of yang power. In fact, the hours before wu and after zi (子, midnight) are considered the best time to practice Daoist exlixir cultivation.  And since heaven is the embodiment of yang,  it’s possible worshipers believe water collected at noon is infused with strong yang energy, thereby giving it the ability to detect the presence of celestial deities like the Great Sage.
J.D. Martinsen contacted me and noted that “drawing noon water” (da wushi shui, 打午時水) is a common practice in coastal China during the Dragon Boat Festival. The water is apparently known for its demonifugic and medicinal properties. In fact, this custom is even practiced in Taiwan where there is a common saying: “A sip of noon water is better than three years of herbal medicine” (wushi shui yin yi zui, jiao hao buyao chi san nian, 午時水飲一嘴，較好補藥吃三年) (Chen, 2011, p. 210). Therefore, this association with warding malevolent influences/sickness may explain why Sun Wukong is connected with noon water. He is after all the exorcist par excellence, as well as a healer.
1) This is noted as early as the fourth-century CE work Wondrous Record of the Golden Casket on the Spirit Immortals’ Practice of Eating Qi (Shenxian shiqi jin’gui miaolu, 神仙食氣金櫃妙錄) (Kohn, 2008, p. 84).
2) See, for example, Clearly (2003), p. 391.
Chen, X. (2011). Taiwan li shi shang de yi min yu she hui yan jiu [The History of Taiwanese Immigration and Social Studies]. Beijing: Jiu zhou chu ban she.
Cleary, T. F. (2003). The Taoist Classics: The Collected Translations of Thomas Cleary, Volume Two. Boston, Mass: Shambhala.
Elliott, A. J. (1990). Chinese Spirit-Medium Cults in Singapore. London: The Athlone Press. (Original work published 1955)
Kohn, L. (2008). Chinese Healing Exercises: The Tradition of Daoyin. Honolulu: University of Hawaiʻi Press.
Wu, C., & Yu, A. C. (2012). The Journey to the West, vol. 1. Chicago, Illinois: University of Chicago Press.
Wu, Z., & Taylor, W. K. (2014). Heavenly Stems and Earthly Branches – TianGan DiZhi: The Heart of Chinese Wisdom Traditions. London: Jessica Kingsley Publishers.