[Xiaomi Mi Band 4 Questions & Answers] _mysiak_:
I've compiled a short list of frequently asked questions seen over various forums or points which were not clear to me (even as a user of MB2). If you find anything missing or incorrect, please let me know.

Q: How to track sleep?

A: Sleep is tracked automatically during night hours, Heart Rate sleep assistance can help in improvement of the detection of various phases. To view the sleep stats, open Mi Fit app and sync the band. Sleep/naps are not detected during day hours.

Q: Does Mi Band have automatic workout tracking?

A: No, workouts have to be started manually either from Mi Fit, or from the band directly.

Q: How to use 24/7 HR with less battery usage?

A: Configure "Automatic heart rate detection & Sleep assistant", detection frequency as desired. Do NOT enable activity detection - it will switch to continuous HR measurements whenever there is some activity detected (e.g. walking). When needed, use manual workout for continuous HR monitoring instead (which will also gather additional statistics).

Q: How to use a 3rd party watch face?

A: The most easy way is to use app like Notify & Fitness, Mi Band tools, etc to apply the watch face directly. Great selection of watch faces can be found here https://amazfitwatchfaces.com/mi-band-4/top. AmazFaces populates the "My band displays" in Mi Fit application.

Q: Is MB4 waterproof? Can I swim/shower with it?

A: Per standard GB/T 30106-2013 (or ISO 22810 : 2010(R2016)), 50m water resistance is rated as suitable for showering, surface swimming and shallow snorkeling. Diving is not recommended. After each submersion in sea water you have to clean the watch/band in fresh water.

Q: MB4 cycles through menu during water activities.

A: Enable lock screen on the band and try avoiding running water in the "down->up" direction. Shower can easily imitate slide up gesture and unlock the screen.

Q: MB4 detects HR when laying on the table or wrapped around inanimate objects.

A: "Signal-to-noise ratio of a real blood flow is sometimes very low so the algorithms are very sensitive in screening for any non-random components in the light variation, and when such are found they are interpreted as HR. So, the algorithms pretty much always find something which is not completely random and interpret that as a HR."

Source: https://www.wareable.com/fitness-trackers/why-heart-rate-monitor-work-on-toilet-rolls-6606

Q: What is behavior tagging in Mi Fit?

A: AFAIK behavior tagging is there only to help developers to make the band more accurate, once you stop the activity, data collected from sensors are uploaded to Xiaomi. It does not impact nor improve your statistics directly and it certainly drains the battery as sensors are being constantly pulled for data. When you start an activity, press the button in the upper right corner - it will switch to real time raw data of sensors.

Q: Is there a hardcoded minimum Heart Rate value (e.g. 47bpm)?

A: Band measures as low as 40bpm (if this value is actually 100% correct is hard to tell as it happens during sleep :) ).

Q: Are there 3rd party apps for Mi Band management? I do not like Mi Fit.

A: M̶i̶ ̶F̶i̶t̶ ̶i̶s̶ ̶m̶a̶n̶d̶a̶t̶o̶r̶y̶ ̶f̶o̶r̶ ̶a̶l̶l̶ ̶3̶r̶d̶ ̶p̶a̶r̶t̶y̶ ̶a̶p̶p̶s̶ ̶f̶o̶r̶ ̶t̶h̶e̶ ̶t̶i̶m̶e̶ ̶b̶e̶i̶n̶g̶.̶ ̶N̶o̶t̶i̶f̶y̶ ̶&̶ ̶F̶i̶t̶n̶e̶s̶s̶ ̶i̶s̶ ̶d̶e̶s̶i̶g̶n̶e̶d̶ ̶a̶s̶ ̶a̶l̶m̶o̶s̶t̶ ̶a̶b̶s̶o̶l̶u̶t̶e̶ ̶r̶e̶p̶l̶a̶c̶e̶m̶e̶n̶t̶ ̶o̶f̶ ̶M̶i̶ ̶F̶i̶t̶ ̶a̶n̶d̶ ̶t̶h̶e̶r̶e̶ ̶i̶s̶ ̶a̶ ̶h̶i̶g̶h̶ ̶c̶h̶a̶n̶c̶e̶ ̶t̶h̶a̶t̶ ̶i̶t̶ ̶w̶i̶l̶l̶ ̶w̶o̶r̶k̶ ̶a̶s̶ ̶a̶ ̶s̶t̶a̶n̶d̶a̶l̶o̶n̶e̶ ̶a̶p̶p̶ ̶i̶n̶ ̶t̶h̶e̶ ̶f̶u̶t̶u̶r̶e̶ ̶(̶s̶a̶m̶e̶ ̶a̶s̶ ̶w̶i̶t̶h̶ ̶M̶B̶2̶ ̶a̶n̶d̶ ̶M̶B̶3̶)̶.̶ ̶O̶t̶h̶e̶r̶ ̶a̶p̶p̶s̶ ̶a̶r̶e̶ ̶o̶n̶l̶y̶ ̶a̶d̶d̶i̶t̶i̶o̶n̶s̶ ̶a̶n̶d̶ ̶r̶e̶q̶u̶i̶r̶e̶ ̶M̶i̶ ̶F̶i̶t̶ ̶t̶o̶ ̶b̶e̶ ̶i̶n̶s̶t̶a̶l̶l̶e̶d̶ ̶a̶n̶d̶ ̶u̶s̶e̶d̶.̶ It is possible to use N&F and some other apps in standalone mode, for more information follow https://www.freemyband.com/ guide (root and no root options available).

Q: I don't see detailed stats (steps, sleep, heart rate) for previous days, only summary in history.

A: When on the detailed screen of the current day, swipe right to navigate to detailed stats of previous days.

Q: Mi Band keeps unfastening itself during sleep or when dressing/wearing backpack etc.

A: Try to wear the band reversed (strap loop away from you, fastening button towards you). Also you can buy a silicone strap keeper (generic 14mm or specifically for Mi Band on Ali/eBay/..) to keep band on hand even when accidentally unfastened.