Always have a spare, sometimes two babies means two monitors.
Last year just before the twins first birthday they both got tonsilitus, they had it for 6 weeks, it was hell. In despiration for more than a minutes sleep and to avoid unison crying (all 4 of us!) we moved little M downstairs. Our lounge became her bedroom, E had the montor upstairs while we were awake and when we went to bed we tiptoed into his room removed the monitor, went downstairs, tiptoed into M’s makeshift bedroom and plugged it in. CRAZY! Why didn’t we just buy another monitor? another case of sleep deprivation leading to a lack of common sense!