Just buy a wirelss video door intercom system,don't need complicated installation,just need a adhesive sticker,you can easily achieve safe and convenience.
Same thing happened to me - wired doorbell stopped working. Bought a wireless doorbell, cost just €20. Brilliant. No wires and can place the bell anywhere i.e. leave in sitting room or if going upstairs can carry bell with me. Simple to instal. Any electrical shop will have different types of wireless doorbells.