The present invention provides an alarm device, a tool, and a control method that can reduce the burden of operating a power switch. An alarm device is applied to an oxygen supply system including an oxygen output section and a supply path that is a path for supplying oxygen from an oxygen cylinder to the oxygen output section. The alarm device 10 includes a power supply 11 having a power switch 112 that can switch on and off the output power, an alarm unit 12 that can output an alarm by electric power, and operates in response to the internal pressure of the supply path. An operating unit 13 that can switch the switch 112. [Selection diagram] FIG.【課題】この発明は、電源スイッチの操作の負担を軽減できる警報装置、用具及び制御方法を提供する。【解決手段】警報装置１０は、酸素出力部と、酸素ボンベから酸素出力部へ酸素を供給する経路である供給経路と、を備える酸素供給システムに適用される。警報装置１０は、出力する電力のオンとオフとを切り替え可能な電源スイッチ１１２を有する電源１１と、電力により警報を出力可能な警報部１２と、供給経路の内圧に応答して作動し、電源スイッチ１１２を切り替え可能な作動部１３と、を備える。【選択図】図３
