About five minutes into the episode, after Ezra sees visions of Maul, Kanan has Sabine put a tracking device on Ezra's wrist comm:
Later, after Maul appears on Atollon, makes a deal with Ezra in which each will share the information he saw when they joined the holocrons in "The Holocrons of Fate," and then leaves with him, Kanan and Sabine are able to follow Ezra using this signal.
On Dathomir, Maul tells Ezra that "the only way to access the knowledge we seek is to merge our minds again." He explains that "I have studied the ways of the Nightsisters and found a spell that suits our needs... to initiate the merge, we, we must each drink this potion." When Maul drinks, his own wrist comm is plainly visible, and it has the same basic design as Ezra's:
Since they opened the holocrons together in "The Holocrons of Fate," Ezra's and Maul's minds have been linked to a certain degree, and in a small way, the similar design of their wrist comms visually indicates this connection between them.
