this thread helped me a lot. Plenty of people shared their experiences. Let me say: "Thank you all, folks!"
So is time to slightly return what I got and share my fresh experiences.
I am newbie in watch repair but not in electronics. I can read plenty of stories here about sensors and amplifiers.
I can read "simple" or "easy" or "cheap" or "work for me" solutions. No one worked for me as I expected .
1. sensor - piezo . All piezos have very low sensitivity. Does not matter of the size - (resonant frequency depends on size).
Most of available circuits are based on a "knock" detector. For watch sensing have very low sensitivity. Also sensor frame construction takes account a lot - because of energy absorption.
Holding piezo in fingers and trying to detect a sound - no way. So finally I decided to use a microphone.
2. sensor - electret microphone (common type). Described problem with a sensor frame construction is much lower and sensitivity is much higher.
What is bad the mic can hear any other noise not just watches. So pay attention to any fans, wind, building works or a colleague typing very hard next you.
3. amplifiers - the sensor supports some signal. Input value extremely depends on where sensor touch your watches. Still is important signal-noise ratio (high sensor signal in very noisy background can be unusable!) not just absolute value of the signal.
Just FYI the ratio between mic sensor attached to closed watches and opened (touched to a watch frame) should be 100times!!!
Signal coming out from the sensor is very low and must pre-amplified about 90dB+ (partially in you external pre-amplifier and partially in you PC or phone).
What is bad and not very suitable for the electronic enthusiasts - high gain amplifier can get easy oscillation. Oscillating amplifier is definitely not the amplifier. Without deep experiences what going on with your amplifier and an oscilloscope tool your are not able solve that problem.
Another problem is any bread board solution hardly can be copied with success (still we are talking about high gain amplifier).
Uffff, too many bad information. Yes I know, sorry. Just sharing mine.
Is there any repeatable solution today?
Yes, exists. I know it from today because finally this solution works for me and is usable without any special tools.
1. microphone pre-amplifier from ebay based on max9814. https://www.ebay.com/itm/MAX9814-Electret-Microphone-Amplifier-Board-Module-AGC-Auto-Gain-ASS/263928751428?hash=item3d73612544:g:~BoAAOSwD5ZZxMVm
2. quitar sensor https://www.ebay.com/itm/Guitar-Acoustic-Clip-line-Pick-up-Pickup-Built-in-Vibration-Sensor-With-1m-Cable/282574713836?hash=item41cac3f3ec:g:EKIAAOSwf~ZZbI6k
3. some shielded cable, 3.5mm connector to your PC or mobile (I used PC because my Xiaomi phone heavy loaded pre-amplifier output. Actually don't know why), 5V power supply - prefer linear and external not USB or 4.5V battery, hot glue, solder station and basic electronic experiences or ask friend.
1. carefully desolder the microphone from pre-amplifier
2. open sensor clip and remove piezo. Drill 9.6mm hole inside (hole depends on removed microphone).
3. cut off the connector from piezo sensor cable and solder on microphone (keep an eye of shielding) and other side connect to pins on pre-amplifier board
4. put microphone into the hole and fix position and cable with hot glue
5. solder on cable connector for your PC or mobile (mobile has 4pin and different connecting than PC - use google.
6. Connect 5V power supply and try out to setup your PC mic input as was previously described in this thread.
How to test entire solution:
Clip on microphone sensor to your opened watches (getting the strongest signal available). Eanable "listening" option in microphone tab. From your speakers you have to hear sound of your watch beating. Preset gains to level below you hear oscillating.
If everything works fine just turn on a timing SW.
Good luck and apologize my bad English
PS: I was trying out to check accuracy colleague of mine OMEGA. Sure unopened. And I was not able to find proper gain level before oscillating. FYI.
PS: Why my phone heavy load pre-amplifier output ... maybe next time.
PS: You can see resistor 392 (3K9) in place of original (2K2). I lost 2k2 during testing.