The title is probably already enough info. Just an example:
Imagine a power button on the front of a computer that is always connected except when pressed, it disconects for a brief moment.
Electronic – What’s the name for a switch that opens its contacts when pressed
switches
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This is variation on my answer to this question. Like Mike, I am also using a P-channel MOSFET. The OP stated: "The Voltage regulator requires Vin +/- 0.3V on the Enable Pin", and "MicroController Output Pin High state is 2.7V Max". Therefore when the battery voltage is above 2.7v, the µC will be unable to supply the required voltage to meet the voltage spec for the Enable lead. So I am using the control lead of the µC to control the MOSFET, which in turn switches the battery voltage (or Vin) to the Enable lead.
Initially, the control lead from the µC is configured as an input. When the button is pressed, battery power is applied through a Schottky diode (keep Vf below 0.3v) to enable the regulator. The µC then configures the control lead as an output and grounds it, keeping the enable lead high through the MOSFET (which keeps the voltage at the battery level). Meanwhile, the button can be used as an input.
The circuit should draw very little power (less than 1 µA) when the µC is powered down, assuming the regulator shuts down completely when the Enable lead is low.
This eliminates the cost of the LTC2954 chip which runs over $2 in 500 unit quantities. This circuit should be under 10 cents in quantity (except for the switch and regulator).
Power draw from a plugged in power adaptor that is not in use, is measurable, but negligible in the long run. A 2 Amp switching supply like that will cost you maybe a buck or two a year, if left unused but plugged in 24/7. Negligible is subjective.
But the supply for that led strip, is just a power supply. It has no off mode, no flashing, nothing fancy. So unless you disconnect the strip, the supply will be powering the strip. Unless you disconnect the supply.
So you need to switch the outlet.
A simple method is a dollar store switched outlet adaptor.
Or a power strip.
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Best Answer
That's called a normally closed pushbutton.
Most pushbuttons are open when left alone, and pushing them closes the electrical connection. These are called normally open. Normally closed pushbuttons do exist, but will be harder to find and more expensive when you do.
Nowadays, pushbuttons are usually just inputs to microcontrollers, so their polarity doesn't matter to their function. The micro can tell whether the button is pressed or released at any time, and then take the appropriate action.
For example, you could use a normally open pushbutton into a micro, which can then interrupt power to something else when the button is pressed. Even without a micro, you could use a relay that allows power to flow when not energized. Pushing a normally open pushbutton would energize the relay, which would interrupt power. This has the advantage of the power and possibly high voltage not being near the pushbutton where you have to worry about proper isolation. The pushbutton also need not be rated for the full power current. It only needs to handle enough voltage and current to energize the relay.