Is it possible to take off your Hijaab when outside if there is no danger of any non-Mahaarim seeing you? I ask this because many sisters go outside in their backyards, without Hijaab when they have very high fences. However, it was put to me that the Jinn can still see us, so their opinion was that this is incorrect.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

It is permissible for a woman to take off her Hijab when she is secure from non-Mahram (marriageable men) seeing her, like when she is at home and other places where men can not see her.

The woman is ordained to wear Hijab in front of non-Mahram men but not in front of the Jinn.

If it is true that she has to wear Hijab in front of the Jinn, then she would be obliged to wear it even when she is inside her own home as it is probable that there are Jinns in it and they could see her.

So this is not true and there is no evidence proving it neither in the Book of Allaah nor in the Sunnah of the Prophet .  

Allaah Knows best.