I want to power 3 hc-sr501 PIR motion sensors with a voltage regulator that can output 5v-1A. If I make such a system, will there be a noise?
Many internet sources like this one claim the HC-SR501 requires less than 50uA (or 0.00005 Amps). Likely this is only in a quiet or quiescent state and current demand may increase initially when power is applied and when motion is detected. Regardless, this is an insignificant fraction of a 2 Amp power supply.
Likely the Atmel 328p will require several times the total current of the 3 PIR sensors added together. Still, the over all current of the described project (1 processor and 3 PIRs) is expected to be far less than half the capacity of a 2 Amp power supply.
It is suggested to keep the PIR to Arduino wires as short as possible to avoid noise. It would be preferable they only be several inches (10s of centimeters). And certainly not as long as several feet (a meter).