A TSA agent may press the button that corresponds to the sex a passenger was assigned at birth, but the passenger's gender presentation may mean using a chest binder, packer, or breast shaper, which the machine then marks as inconsistent with the expected algorithm for the passenger's sex, thus triggering an "alarm." Alternatively, the agent may press the button corresponding to the passenger's presenting gender rather than the sex they were assigned at birth, which poses its own problems: A "passing" trans woman's penis, for example, will register to the machine as suspicious.
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