From the ground floor it reaches perfectly to the second floor. The sound is loud. Absolutely satisfied for now.

I bought the doorbell not for the classic use. My mother lives in the apartment and my sister lives upstairs. She is not very tech-savvy to answer with a mobile phone, and she has mobility problems to go downstairs. She might have left the wireless somewhere in the house, you understand. So, I thought the following:
The doorbell will be the help button, and I placed the speaker on the upper floor. So, she presses the button, my sister hears the sound, and she understands that she needs to come down.
The doorbell-transmitter works with a 12V 23A battery that is already inside the device, but you need to open the lid to remove the protective paper. The speaker-receiver requires 2 AA batteries of 1.5V, which are easily found. It is a powerful speaker, it has 32 melodies that you can change which one you will hear from a button inside above the battery compartment.
You can screw it on the wall, place it on the table, or hang it with the built-in hook it has!
Apart from the sound, it has a small red light, probably for those who have hearing problems.
Overall, I was impressed by its low price.

It works perfectly for 9 years.

- Relatively good range (if you place it on a metal door, the range is limited). Tested at 15 meters, it works perfectly if there is no metal construction in between. If there is a metal surface, it works perfectly at around 8 meters and after 3 walls. However, the sound easily covers the distance difference. You don't need to have it close to you. Even if you install it on the back side of the door, the sound can be heard clearly after 10 meters and with 2-3 intermediate walls. I haven't tested it at 30 meters.
- It has playful but also serious sounds. However, if the batteries run out, the playful sounds become distorted while the serious ones remain perfect.
- The battery of the transmitter (outside the door) was replaced once (in 7 years).
- The batteries of the doorbell (inside the door) last for about six months. They need to be changed twice a year with sparse usage.
- There is a "little hook" on the back side of the doorbell that facilitates its placement even on a cable.