It's not so nice, i am only a beginner in electronics, but it just works.

Components: (with ebay prices, somewhat more from elsewhere)
- ESPEasy: the main component, priceless
- Wired Alarm Strobe 12V Siren Security: 3$
- D1 mini Development Board clone: 3.45$
- 10cm Micro USB Charger Cable: 1$
- MOS FET Trigger Switch Drive Module PWM Regulator Control Panel: 1$
- DC-DC Adjustable Voltage Step Down Regulator Module: 1$
- DC 12V 0.5A 500mA Power Supply: 2.5$
- some cable and time to assemble
Optional component:
- HTU21D for extra 2.33$ - just for fun, and because it is supported fully by ESPEasy

Before:

After:

Wiring:

I'am controlling the MOSFET relay gpio through GlobalSync from another ESP, but also works by MQTT, URL... anything that ESPEasy is capable of.