4.
In my view it not taxable on RCM basis. Please refer Sec 9(3) of CGST Act 2017. Sec 9(3) is reproduced here under for your ready reference.
(3) The Government may, on the recommendations of the Council, by notification, specify categories of supply of goods or services or both, the tax on which shall be paid on reverse charge basis by the recipient of such goods or services or both and all the provisions of this Act shall apply to such recipient as if he is the person liable for paying the tax in relation to the supply of such goods or services or both.
So, all the provision of the act will apply to recipient and in tax payable in relation to the supply. As per Sec 7(1) (a) all forms of supply of goods or services or both such as sale, transfer, barter, exchange, licence, rental, lease or disposal made or agreed to be made for a consideration by a person in the course or furtherance of business;
Security service at home of registered person is not in the course or furtherance of business but its personal in nature. GST is basically tax on business. The said transaction is personal in nature. In my view GST on RCM will not be applicable.