There is nothing wrong with a woman uncovering her hair in front of her mahrams and in front of other women, and when she is alone in her house. This is something on which the scholars are agreed and is what Muslim women have done since the time of the Prophet (blessings and peace of Allah be upon him) and up to the present.
With regard to the claim that the Shaytaan plays with a woman’s hair if she uncovers it in her house, this is a false claim for which there is no evidence and no hadeeth or report has been narrated concerning it. So it is not permissible to make this claim or approve of it, or to transmit it to people. Allah, may He be exalted, says (interpretation of the meaning):
“And follow not (O man, i.e., say not, or do not, or witness not) that of which you have no knowledge. Verily, the hearing, and the sight, and the heart of each of those ones will be questioned (by Allah)”
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked the following question:
When the muezzin gives the call to prayer and a woman has her hair uncovered and is in her house, or in her family’s house, or in a neighbour’s house, where no one can see her except her mahrams or other women, is that haraam? Do the angels curse her for the duration of the adhaan?
This is not true. A woman may uncover her hair even when the muezzin is giving the call to prayer, so long as no non-mahrams can see her. But if she wants to pray, then she has to cover all of her body except her face, although many scholars grant a concession allowing her to leave her hands and feet uncovered too. But to be on the safe side she should cover them too, except for the face; there is nothing wrong with leaving it uncovered. This applies when there are no non-mahram men around her; if there are, then she must also cover her face, because it is not permissible for her to uncover it except before her husband and mahrams.
And Allah knows best.
(Source - Islam Q&A)