The Ketotek KT4000 is a dual‑relay plug‑in temperature controller for automating heating and cooling devices. It uses a waterproof NTC probe (3 m) to sense temperature and independently switches two 10 A relay outlets labeled for cooling and heating. The control range is −50 to 99 °C (default 20 °C) with 0.1 °C resolution and ±1 °C accuracy. Heating and cooling differentials are adjustable from 0.5 to 20 °C (default 2 °C). The unit operates on 220 Vac ±15% at 50/60 Hz and draws ≤3 W. Typical applications include aquariums, incubators, and small greenhouses where either air or water temperature must be maintained near a setpoint. Front‑panel buttons provide straightforward parameter entry.