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I am using an inductive proximity sensor having an operating voltage of 5V with raspberry pi 3B+. Sensor has been given 5V from Pi. On sensing metal, output of this sensor is approximately 4.5-5Volts. I have connected this output to one of GPIO pins of raspberry pi. Raspberry Pi is working fine. But as per specifications, Pi can not tolerate voltage above 3.3V. I am not getting how could GPIO pin tolerate voltage above 3.3V. Is this possible?

Jashanjot Kaur
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    Yes, but only once. After that the GPIO pin is broken at best or the Pi dead at worst. If you are lucky, the Pi lives in a state where you think everything is fine but will encounter random crashes and kernel panics. This did happen to me after I provvided a 5V signal to a GPIO pin. – kwasmich Mar 13 '20 at 07:13
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    Use a logic level shifter to avoid such problems. – kwasmich Mar 13 '20 at 07:14
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    @kwasmich... That's why I am confused. Pi should be dead the moment it gets above 3.3V. I am using this sensor with Raspberry Pi since 9-10 months. I am surprised that Raspberry Pi is working fine without any issue. Still I will use voltage divider to avoid any sudden crash. – Jashanjot Kaur Mar 13 '20 at 07:25
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    It is like getting a bullet into the head. Some live on happily, some show signs of brain damage right away and some are instantly killed. Just because your Pi still works, does not mean that nothing went wrong. Just don't consider your Pi 100% reliable any more. Anyway it also depends on the exact output signal - is it a short pulsed one or a constent high like in PIR motion sensors; what is the resistence of the wire and so on. All those factors have influence on the outcome of such a small mistake. – kwasmich Mar 13 '20 at 07:31
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    @kwasmich... Thanks for your reply and such a relatable example of bullet in head. – Jashanjot Kaur Mar 13 '20 at 07:38
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    If you take an electronic engineering course and analyse the circuit you have connected and the detailed specs of the Pi you may be able to work out why. The rest of us (including those with Electrical Engineering qualifications) follow the specifications and don't worry about out of spec behaviour. – Milliways Mar 13 '20 at 09:14

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