noun
alternate device
Computing term for a backup or secondary device that takes over when the primary one fails or is unavailable.
システムは、主装置が故障した場合に交替装置に自動的に切り替わる。
The system automatically switches to the alternate device if the primary device fails.
予備装置 is a more general term for a spare or standby device, while 交替装置 specifically implies an alternate device that takes over operation.
Compound of 交替 (alternation, change) and 装置 (device, equipment).