Android - How to call my own phone with a loud ringing tone (in order to find it in my house) even if it is in silent mode?
You may consider using Google's Find My Device (web version, app). I would not suggest a third-party app from unreliable sources (although you can't trust Google as well :p).
You can automate the process. Install Macrodroid on the old phone, open it and add a macro. Then follow the steps below:
In the Triggers tab, in the Call/SMS section, select "Call Incoming', then "Select Contact(s)". Choose your phone number.
In the Actions tab, in the Volume section, select "Volume Change". Give the appropriate permission to Macrodroid. Select "Volume Change", enable Ringer and set the volume percentage.
In the Constraints tab, in the Screen and Speaker section, select "Ringer Volume", then Silent.
Save the macro, give it a name.
Is there a way to make one specific number always ringing loud? (even if the phone is in silent mode)
Another solution could be that instead of putting the phone in silent mode, you can set the default ringtone to a silent audio file. Then, you can set a normal ringtone for the contact of the number you want to call from.