Easy way - (If you don't want to mess with electronics/electrical)

Buy the standalone smoke detectors (mentioned previously), 433Mhz receiver (e.g. DVB-T FM DAB) and create your own smart hub using open-source home automation suite like (https://www.openhab.org/ or https://www.home-assistant.io/)  to monitor and notify alarm.

Bit of effort -

Buy an individual sensor like MQX (X for different types of smoke, gas etc.), connect it to a MCU like NodeMCU, connect a buzzer and power supply, create your own smart hub (mentioned earlier).

I will do a detailed write up on my personal blog later and share you the link.