"Secret Tape" is the fith and final track SUNMI wrote for her second EP/first relase after debut; WARNING.
Depicting an emotionally intimate moment between Sunmi and the person she is with, the lyrics narrate her drunken moment of transparency; that even if they both say 'senseless things', the time that they spend together still matters. It's a plead for them to spend more time together and to speak truthfully despite the vulnerable nature of doing so. She asks them not to tell anyone what they've spoken about since it's their 'secret' and theirs alone.
The song begins with a sample from Sunmi's Sony Walkman which she bought in late 2018 for Seulgi (슬기) of Red Velvet and herself. They met in a reality TV program called Secret Unnie (비밀 언니) which pairs celebrities together in hopes of a friendship to form over the course of seven episodes.