https://eclecticlight.co/2025/03/16/last-week-on-my-mac-the-myth-of-liquid-detection/ Skip to content [eclecticlight] The Eclectic Light Company Macs, painting, and more Main navigation Menu * Downloads * Freeware * M-series Macs * Mac Problems * Mac articles * Macs * Art hoakley March 16, 2025 Macs, Technology Last Week on My Mac: The myth of liquid detection Macs have developed their own mythology, and this week I unintentionally came across a myth that developed over a year ago. Like so many it was born from a chance observation, this time of a new background process that appeared on 25 October 2023 in macOS Sonoma 14.1, and was reported in 9to5Mac on 3 November 2023. Discovery The process in question is liquiddetectiond, and as 9to5Mac's headline claimed, it meant that "Macs can now inform Apple if any liquids have been detected in the USB-C ports". That article argued that "it seems more likely that the data collected by this daemon will be used for technicians to determine whether a Mac is eligible for free repair." "Putting a digital liquid detector on USB-C ports is just another way to ensure that technicians are right about claiming that a Mac has been exposed to liquids." That, and a couple of linked reports elsewhere, brought a small flurry of comments about how typical this was of Apple, then all went quiet until 9to5Mac's article was picked up by Hacker News on 9 January 2024 and generated 340 comments. Predictably, most either castigated Apple's behaviour or disappeared down rabbit holes about unrelated topics. Among them, though, was one precious insight: "It prevents the device from applying/draining power from any pin in such a state, mainly to reduce corrosion of the contacts and increase longevity." By the middle of January last year, the story had gone cold, and everyone must have gone away with their worst fears confirmed. You couldn't even get a USB-C port damp in your Mac any more, as Apple would use that as an excuse to void your Mac's warranty. Documentation Apple's first word on the subject seems to have been in a support note published on 23 November 2024, which passed largely unnoticed. This announced liquid detection as a feature new to macOS Sequoia when running on only the following models: * MacBook Air M3 and later * MacBook Pro with M3 Pro or Max * MacBook Pro with M4 base, Pro or Max none of which had been released at the time of 9to5Mac's report, although the second were released four days later, on 7 November 2023. If there's liquid in one of their USB-C receptacles (ports) when a USB-C cable is connected to it, this new sensor should detect it and alert the user, advising them to shut the Mac down, disconnect all cables and leave it to dry. This is in addition to, and separate from, what Apple terms Liquid Contact Indicators (LCI), that have long been fitted to laptop Macs and some Apple wired and wireless keyboards "to help determine if these products have been exposed to liquid," according to this support note. Was Apple just making excuses, or was this new liquiddetectiond service intended to benefit the user? Evidence I stumbled into this innocently last week when I was looking at Accessory Security, a feature confined to laptop Apple silicon models. By chance, the laptop I was using was a MacBook Pro M3 Pro, one of the few in which liquid detection works. There, on several occasions in its log, after connecting a Thunderbolt cable, its liquid detection system checked that the USB-C port was dry, in a series of log entries like: 0.887 liquiddetectiond Starting LDCM Now 0.887 liquiddetectiond LDCM Discovery is enabled. 0.889 liquiddetectiond LDCM - Matched with V4... 0.890 liquiddetectiond LDCM - checkIsReceptacleEmpty: 0 0.890 liquiddetectiond LDCM - Handling LDCM interrupt event for port 2 0.890 IOAccessoryManager IOPortFeatureLDCMUserClient::_copyData(): Copying LDCM data... (target: Port-USB-C@2/LDCM) 0.890 liquiddetectiond LDCM - Feature Status: 0, Completion Status: 0, Measurement Pin: 0 Mitigations Status: 0, Wet: 0, Wet State Duration: 0 0.890 liquiddetectiond LDCM - checkIsReceptacleEmpty: 0 0.890 liquiddetectiond LDCM: liquidDetected: 0, receptacleEmpty: 0, shouldShow: 0 (Times given in seconds elapsed.) But on my more recent Mac mini M4 Pro running Sequoia, all I saw was that LDCM is not supported on this device. Attempts to connect over the network are obvious in the log, and on not one of the occasions that liquid detection was performed did that MacBook Pro try to connect to any remote site. Maybe its reports could have been embedded in other analytics data passed to Apple later, but there was absolutely no evidence that the results of liquiddetectiond went beyond the confines of my Mac. This demonstrates the importance of testing out hypotheses, and of reading the log. Even without the benefit of Apple's recent support note, it should have been easy to demonstrate this behaviour, yet no one seems to have attempted to. Explanation Claims made of the role of liquid detection in USB-C ports also don't make sense. As with most laptop manufacturers, Apple already builds Liquid Contact Indicators into components of laptop Macs within their case. These are most frequently affected by spillage of drinks on a laptop's keyboard, resulting in any of a wide range of water-based liquids from coffee to cognac entering the case. That often results in extensive damage to the logic board and other components, that are expensive to replace. But a damp USB-C port is quite a different matter. It could occur in a laptop that had been out in the cold and was then brought into a warm and more humid environment, the same sort of conditions that steam up your spectacles. Over time, that could lead to corrosion of the contacts in the USB-C ports, and unreliable connections. Because each release of macOS is identical across all models of Mac, although only a few of the most recent models feature liquid detection sensors in their USB-C ports, the liquiddetectiond service runs in the background of all Macs running Sequoia. It's to be found inside /System/Library/CoreServices/liquiddetectiond.app, which isn't even a bundle, just its Mach-O binary and an image of the warning sign displayed. It's run through its LaunchDaemon com.apple.liquiddetectiond.plist, which you'll also find in the SSV of every Mac. As is so often the case, the truth behind the myth is more prosaic, and doesn't involve Apple secretly capturing data from your Mac, nor conspiring to dodge warranty repairs. In fact, if you look at the warranty terms of pretty well every other laptop manufacturer, they too exclude damage caused by liquid ingress, as demonstrated by their Liquid Contact Indicators. And some are also starting to fit similar liquid detection sensors in their USB-C ports. But don't let those get in the way of a good myth. Share this: * Twitter * Facebook * Reddit * Pinterest * Email * Print * Like Loading... Related Posted in Macs, Technology and tagged Apple, liquid detection, liquiddetectiond, MacBook Air, MacBook Pro, macOS 15, Sequoia, USB-C. Bookmark the permalink. 12Comments Add yours 1. 1 [c2ae248b67e1] Extrawdw on March 16, 2025 at 10:50 am Reply While it is unlikely that the service uploads data to Apple servers, liquid detection history might still be available in the Mobile Resource Inspector which a Genius Bar will use for diagnostics. As USB PD goes to 24V or even 28V, adding liquid detection will be necessary at some point, but rejecting warranty because of this is not okay to me, hope they won't do that. LikeLiked by 2 people + 2 [87cc8acbb0b9] hoakley on March 16, 2025 at 12:54 pm Reply Do you any evidence to support your claims? Or is this just the FUD on which to perpetuate myth in the face of the facts I have laid out above? Howard. LikeLike + 3 [2c27638b7fbb] Simon on March 16, 2025 at 3:21 pm Reply I hope so as well. The article itself points out that we do not know with certainty if Apple will use this information that way or not ("Maybe its reports could have been embedded in other analytics data passed to Apple later..."). Don't be discouraged by a rude response. Such a reply reflects back on the thin skin of the person being rude, not on you. LikeLiked by 1 person o 4 [87cc8acbb0b9] hoakley on March 16, 2025 at 3:30 pm Reply Simon, There's nothing "rude" in my response. I asked two simple questions: - first for evidence, which is what this is all about. Anyone can ask questions, but few seem in the least bothered about answering them. Do you have any answers? - then, the whole point of this article. Fear, uncertainty and doubt (in case you don't know what FUD is) is exactly why we need to go to the facts and not invent these myths. Now if you have any factual evidence to contribute, please do so. Not yet more FUD, thank you. And cut out the ad hominems, please. Howard. LikeLike 2. 5 [d24ad2916026] Francois Schiettecatte on March 16, 2025 at 12:17 pm Reply For what it's worth, I have had damp USB-C port warnings on my iPhone when I plugged it in to charge after a (wet & snowy) hike, I assumed it was to prevent shorting. LikeLiked by 1 person + 6 [87cc8acbb0b9] hoakley on March 16, 2025 at 12:57 pm Reply Thank you. Yes, iPhones are different as they are designed, built and tested to be waterproof. I believe this is standard in all iPhones with USB-C ports for the same reasons as given above. Howard. LikeLike 3. 7 [29e74abbac6d] Ingo on March 16, 2025 at 6:22 pm Reply I suppose Apple uses a feature that is described in Appendix A "Liquid Corrosion Mitigation Mode" of the USB Type-C Cable and Connector Specification, Release 2.4 (October 2024). I don't know which release of the standard introduced that feature. Release 2.0 from August 2019 gave us "Audio Adapter Accessory Mode" in Appendix A instead. That has been declared as deprecated nowadays. Additionally I suppose models that support it have got the proper port controller. Development of the MacBook Pro M3 Pro/Max and MacBook Air M3 finalized a lot later than that of the MacBook Pro 14 inch M3, iMac M3 and so on. That's why the MacBook Air M3 supports it and none of the other models using the M3 SoC. That's not the only difference. The FCC-version of Wi-Fi port of the MacBook Air M3 and MacBook Pro M3 Pro/Max support the FCC equipment class "6CD" ("Dual Client Mode" in the 6 GHz band with support for Low Power Indoor Access Points and Standard Power Access Points; only the latter are allowed to operate outdoors in the 6 GHz band). The other models using the M3 SoC are capable to use the Low Power Indoor Access Point only (equipment class "6XD"). LikeLiked by 1 person + 8 [87cc8acbb0b9] hoakley on March 16, 2025 at 7:17 pm Reply Thank you, Ingo - fascinating additional detail, which I didn't know for the models or their Wi-Fi. The title of that Appendix is entirely consistent with Apple's description. What I can't understand is how, with what we know now about the two types of sensors, they can still be confuddled. Liquid Contact Indicators don't alert the user, who already knows of the problem, but provide evidence for the service technician as to what occurred at some time in the past. The USB-C liquid detection sensor alerts the user before power is applied to a USB-C receptacle, so that they can take action to prevent any damage or corrosion occurring. One is evidential, the other preventative. Howard. LikeLike 4. 9 [01b0fad51f3b] Warren Nagourney on March 16, 2025 at 9:51 pm Reply There appears to be a lot of FUD circulating in Apple forums lately. One is a lot of fury about Apple Intelligence, particularly as it applies to Siri improvements. Perhaps it is a "blowing off of steam" due to the recent absolute debacle in US politics and governance. While I think it is necessary to hold Apple's "feet to the fire" when appropriate, I am delighted by all of the offerings in recent Mac hardware, which to me is the most important thing they do even if it doesn't bring in the most revenue. Thank you for debunking the FUD over water detection. LikeLiked by 1 person + 10 [87cc8acbb0b9] hoakley on March 16, 2025 at 10:26 pm Reply Thank you. I agree, and sympathise - we had 14 years of slightly slower destruction including Brexit, and are only now starting to reconstruct our lives. Howard. LikeLike 5. 11 [b221c18c3553] David C. on March 17, 2025 at 10:35 pm Reply It appears that liquid detection is a feature of many USB power-delivery chipsets. The purpose is to cut off power delivery when water is detected, in order to prevent current from going where it doesn't belong, causing damage. Here's a video from Texas Instruments about liquid detection in their chips: https://www.ti.com/video/6361924600112 LikeLiked by 1 person + 12 [87cc8acbb0b9] hoakley on March 17, 2025 at 10:48 pm Reply Thank you. Yes, indeed, as I have been trying to explain all along, and I gather TI is now the leader in these. Howard. 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