Most pacemakers have a sensing device that turns itself off when the heartbeat is above a certain level. It turns back on when the heartbeat is too slow.

大部分起搏器有感受装置，当心率超过一定水平时自动关闭，当心率过慢时打开，这叫做按需式起搏器。

youdao

As with the Glo, it's possible to snap the back of the device off, but unlike that larger reader, there's another level underneath that needs to be unscrewed if you want to swap out the battery.

ENGADGET: Kobo Mini review: does the world need a smaller e-reader?