Have you looked at something like a Ring Doorbell? 
You could then plug in a Speaker upstairs (volume adjustable) without being too loud downstairs. 

These things are good, cheap and have adjustable volume:

https://www.noelleeming.co.nz/p/swann-plug-in-door-chime/N195386.html

Just get a wireless doorbell and buy multiple recievers for it. I have done that back when couriers were wanting signatures, plugging the recievers into smart sockets so that they turn off when the pests tend to be out ringing bells soliciting donations or spreading their word.

ada101:

can anyone recommend a Loud Doorbell (preferably with  adjustable volume). My current wired doorbell sound is too soft for me to hear when I am in the upstairs bedroom.

I have a 20dB hearing loss and need a LOUD doorbell. 😬

After wasting time, money and energy installing conventional wired doorbells, I have found the perfect solution:

PBTech - Brilliant Smart Kinetic Self-powered Wire-Free Doorbell with Chime

 

With a separate receiver and wireless kinetic push button that can deliver a strong signal up to 30m, never miss a customer or visitor with this battery-free and total wireless doorbell.

 

- A compact door chime system that's completely wireless.
- Easy wireless installation, receiver unit plugs into mains power.
- Doorbell runs from kinetic energy with no batteries required & up to 30m range.
- Battery-free push button with up to 100,000 press lifetime.
- IP44 Water-resistant push button.
- 4 Levels of adjustable volume with 38 customisable chime sounds plus a silent mode

 

The mains-powered chime/receiver can be moved to any power point in the house, without "forgetting" its settings (the correct chime and volume).

Problem solved!  🙂

Sideface:

I have a 20dB hearing loss and need a LOUD doorbell. 😬

Many thanks to all the members who replied (some whacky solutions) I think I will try this

PBTech - Brilliant Smart Kinetic Self-powered Wire-Free Doorbell with Chime

get a dog... 

... a small dog will hear for guest and alert you

... a big dog will scare them away!

Plenty of dairies around NZ with cheap Jaycar / DSE / Mitre10 doorbells that are hideously loud and annoying.