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I want to install those movement sensors in my house in replacement for the old light switch. I want to use those from elevator halls which has a 3 way switch to leave on, leave off and leave monitoring.

The thing is: is the sensor energy consumption lower than a 15w to 25w white cold lamp in the hours that I simply leave it on when nobody is around?

These sensors are still expensive in my country. So I will install them only if it's worth the energy economy on long terms.

Edit1:

This is the kind of sensor I am speaking of:

enter image description here

And this is the bulb I am speaking of:

enter image description here

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It would depend on the sensor... –  Ecnerwal Mar 30 at 21:21
    
I edited the question to point on the right kind of sensor. –  EASI Mar 31 at 0:19
    
What is the exact model? The power consumption of a occupancy sensor tends to be low. Measured Field Performance and Energy Savings of Occupancy Sensors: Three Case Studies cites a source that states the power usage of the sensor is 0.002W for PIR types. The same type as the one pictured above. –  Dan D. Mar 31 at 0:57

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Can't find that one. Another company's model that gives numbers (after looking more - MANY don't, which seems sketchy) claims 10mA @ 24v, or 0.01A x24V = 0.24W - less than 15, yes; Quite a bit more than 0.002, though. Whether it's actually worth buying (since you mention that it's expensive) would depend on how much you pay for power and how many hours it would save you 14.75W (or so) - it might take many years to pay for itself, unless your power is also very expensive.

This link has a rather more pessimistic assumption about the sensor at ~3W or so.

And this link has some specific numbers from another brand, ranging from 0.06W to 1.04W (1.04W is a dual-sensor/ ultra-sonic/PIR - highest is 0.18W for PIR only)

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