Ruling on women praying in the mosque when they cannot see the imam or the men praying behind him
Question

                What is the ruling on the prayers of women in mosques where they cannot see the imam or the men praying behind him, and they can only hear his voice?.
Praise be to Allah.It is 
    permissible for women, and also for men, to pray with a congregation in the 
    mosque even if they cannot see the imam or the men praying behind him, if 
    they are able to follow the imam. If the voice reaches the women in their 
    part of the mosque and they are able to follow the imam, then it is valid 
    for them to pray in congregation with the imam, because it is all one place, 
    and it is possible to follow either hearing the voice through loudspeakers 
    or hearing the imam’s voice directly, or by hearing the voice of the one who 
    repeats the imam’s takbeer. It does not matter if they cannot see the imam 
    or the men praying behind him. Rather some of the scholars stipulated that 
    one should be able to see the imam or the men praying behind him if one is 
    praying outside the mosque. The fuqaha’ said that the prayer of one who is 
    praying outside the mosque is only valid if he can see the imam or the men 
    praying behind him. But the correct view in my opinion is that it is not 
    valid for a person to follow the imam from outside the mosque, even if he 
    can see the imam and the men praying behind him, if there is a place in the 
    mosque where he could pray. That is because the purpose of praying in 
    congregation is to bring together the place and the deeds. But if the mosque 
    is full and those who are outside the mosque  pray with the imam and are 
    able to follow him, then the correct view is that it is permissible for them 
    to follow the imam, whether they can see the imam or not, if the rows are 
    continuous. End quote from Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen 
    (15/213) 
And Allaah knows 
    best.