mòshēngrén qiāomén shuō chá shuǐbiǎo, diànbiǎo huò ránqì shí, búyào jízhe kāimén

陌生人敲门说查水表、电表或燃气时，不要急着开门。

When a stranger knocks on the door claiming to check the water, electricity, or gas meter, don't rush to open it.