The song On Guard by Lauren Jauregui is about being cautious and protective of one's heart when it comes to romantic relationships. The lyrics speak to the idea of trusting one's intuition and taking time to get to know someone before fully opening oneself up to them. The song also touches on the pain of past heartbreaks and the importance of keeping one's guard up to prevent further hurt. The overall message is one of self-preservation and being aware of who one allows into their heart.