Downhole sensor apparatus and related systems, apparatus, and methods

A downhole sensor apparatus comprising:

• a structure carrying a circuit board, the structure configured to be inserted into a recess in a tool on a drill string;
• one or more sensors coupled to the circuit board;
• a cap over the structure, the cap secured to the tool and configured to be exposed to an environment around the tool;
• a data port disposed through the cap, the data port electrically coupled to the circuit board and configured to transmit data from the one or more sensors to an external device, without removing the cap from the tool;
• a removable plug disposed through the cap over the data port, wherein the plug is configured to block access to the data port and to protect the data port from the environment around the tool when installed and the cap is configured to provide access to the data port when the removable plug is removed;
• and
• a securing element configured to engage a complementary feature in the recess in the tool, the securing element configured to secure the structure to the tool.