In an aspect, in general, an apparatus includes an electrically conductive housing including a first portion and second portion, the first portion including electronic circuitry. An electromagnetic shield separates the first portion and the second portion and is configured to electromagnetically isolate the electronic circuitry of the first portion from the second portion. The electromagnetic shield includes a plurality of electrically conductive walls partially separating the first portion and the second portion, a plurality of electrically conductive spring loaded fingers extending from an end of at least one of the plurality of electrically conductive walls and configured to contact an inner surface of the housing. Together, the plurality of electrically conductive walls and the plurality of electrically conductive spring loaded fingers separate the first portion and the second portion.