我忘了带钥匙出门。

Wǒ wàng le dài yàoshi chūmén.

I forgot to take my key when I left.

记得带钥匙出门。

Jìde dài yàoshi chūmén.

Remember to take the key when you leave.

我的钥匙不见了！

Wǒ de yàoshi bú jiàn le!

I lost my key!