Keys generally act as symbols of unlocking or finding answers, but for Oskar, keys specifically involve unlocking barriers between people, allowing him to forge connections with others. Early in the novel, Oskar’s mom asks him not to make copies of their house key because it’s dangerous to let strangers in their house, which also serves as a metaphor for the danger of letting people into one’s life because of the harm they can cause. Oskar believes that finding what the mysterious key unlocks will bring him closer to his dad because keys grant access to people’s lives, and he finds the key in his dad’s closet. Oskar hangs the key next to the house key near his heart to symbolize keeping his dad close and their emotional connection. However, over the course of his quest, the key actually brings Oskar closer to New York as a city and the people who live there. A visual representation of this occurs when Oskar flirts with Abby Black and has her hold the key so that they can stand close. Furthermore, the key takes Oskar to the boroughs outside of Manhattan for the first time, expanding his worldview and allowing him to encounter people from different walks of life.
For Thomas, doorknobs represent how locked inside himself he has become, isolating himself from those around him. Thomas burns his hands on the doorknob to his old house in Dresden in his desire to pursue Anna, literally closing the door on his family and shutting away their connections forever. The doorknobs throughout the notebooks in which Thomas writes his letters to his son show just how deeply inside he has shut his feelings. However, when readers turn the novel’s pages with images of doorknobs on them, they mimic the act of opening doors, symbolizing the hope that Thomas could choose to open himself up to life again, reconnect with Grandma, and be a grandfather to Oskar. Similarly, when Grandma allows Thomas to watch Oskar through the keyhole, Thomas is still shut out from connecting with his grandson, but a possibility remains that the door between them could be unlocked. Doorknobs thus lock feelings away, but they may also unlock personal connections.
Oskar hides the family phone after his dad’s last message because it symbolizes what he believes is his failure to protect and support his dad. In his confession to William Black, Oskar explains that he believes his dad needed him to pick up the phone in his last moments for comfort and support. Oskar often tries to take a parental role in his relationships with his mom and grandmother, citing protecting them as one of his very reasons for being. He claims in Chapter 3 that he hid the phone in order to protect his mom from hearing the message, and this action has the double meaning of hiding Oskar’s failure to protect his dad while making up for it by protecting his mom. Oskar treats the phone messages as symbolic of his dad. Before he embarks on his quest for the lock, Oskar listens to his dad’s last messages, as if to connect with him again. He describes the experience of hearing his dad’s voice as a light in the darkness, evoking the way his dad used to give him answers for how to cope with the darkness of the world.