CrossRoads:
Can your IR sensor be setup to output a low level signal when something is close? If, use that to create an external interrupt on D2 or D3 (on Uno for example) to wake up from power down sleep mode.
Well I've not implement it yet but only chose it. I want to DIY it, but currently still can't imagine how to design so that in sleep mode really only IR eats the battery. Would appreciate any hint.
This is my choice of IR bumper switch:
