And in addition to what defragster says, even on the Teensy 3.2/3.5 which does support 5v tolerance on the digital pins, any voltage above 3.3v (or the analog reference voltage if you use that) will be read as the maximum value. So for instance, if you have a Teensy 3.2, and you do an analogRead on pin A0, if the voltage is 3.3v it will read 1023. If the voltage is 5v, it will still read 1023.