1. Yes, we can collect ECG from fingers. Following paper provides you an idea about the measuring technique.

Unveiling the Biometric Potential of Finger-Based ECG Signals

ECG from hands (cornell.edu)

2. Piezoelectric sensor can be used.

pl. read: Piezoelectric extraction of ECG signal | Scientific Reports (nature.com)

3.Which algorithm can we use to emit noise?

pl clarify the question

Yes, you can, assuming you get a differential signal between left an rigth fingers. No ECG possible with optical fingertip.

For ECG direct measurement you need two electrodes on the skin ou under the skin (implant).

If the electrodes are close to the heart the signal amplitude is higher.

A distance of at least 2cm is usually advised to get an acceptable signal to nose ratio (SNR).