In this excerpt from the Vijnana Bhairava: The Manual for Self Realization Swami Lakshmanjoo explains a śāktopāya technique for revealing the formation of the nature of Bhairava by means of Bhairavī (Bhairavī means, uninterrupted awareness). How to maintain uninterrupted awareness?
भैरवि व्यज्यते वपुः ॥२५॥
bhairavi vyajyate vapuḥ // 25 //
Antar bahir, internally or outwardly (vāpi means “or”), internally or outwardly, marutaḥ, this energy of breath, when [it] is followed by two voids by returning back to two ethers, viyat yugma ānuvartanāt, by maintaining the uninterrupted awareness there–[that] means “bhairavyā”, by means of Bhairavī (Bhairavī means, uninterrupted awareness)–when You maintain uninterrupted awareness in these two voids (internally and externally; there is an internal void and an external void), ithaṁ, by this way of treading on this process (ithaṁ, by this way), bhairavasya vapuḥ vyajyate, the formation of the svarūpa [nature] of Bhairava is revealed (vyajyate).
“Bhairavi” is āmantraṇaṁ.71
O Bhairavī, O Pārvatī, here, You have not to recite ‘so’72 or ‘haṁ’. It is without the recitation of ‘sa’ and ‘ha’. It is only awareness that functions here.
It is why this is śāktopāya. This can’t be āṇavopāya because you have to maintain awareness only, no recitation of mantra. Only you have to [inhale] and [exhale] breath and see where are these two voids.73
DEVOTEE: Between going out and coming in?
SWAMIJI: Between going out and coming in. Here74 and in the heart.
JOHN: In āṇavopāya, there is an object.
SWAMIJI: Because [there is an] object [and] there is mantra also.
JOHN: But there is not an object here.
SWAMIJI: There is no object. It is why it is called here śāktopāya.
70 Swamiji preferred “anuvartanāt” to “anivartanāt”.
71 Vocative case.
72 That is, ‘saḥ’. According to the Sanskrit rules of phonological processes that occur at word boundaries (sandhi), visarga (‘aḥ’) followed by a voiced consonant becomes an ‘o’.
73 Swamiji emphasized that these are two “voids”, not two “gaps”.
74 Referring to the external point, bāhya dvādaśānta. A technical term in Kashmir Shaivism, literally meaning “twelve finger spaces.” In this case, it refers to bāhya dvādaśānta, the starting point of breath outside (bāhya) the body, twelve finger spaces from the center of the eyebrows.