An employer's best legal protection with regard to electronic surveillance of employees is to:

Consent is a cornerstone of lawful workplace monitoring. Employers must obtain written acknowledgment from employees if surveillance (e.g., cameras, keystroke logging, emails) is used, particularly in jurisdictions with stricter privacy laws.

Extract from HRCI-aligned HR knowledge (Risk Management):

SPHR-level compliance frameworks require that “employee surveillance policies be transparent and consent-based.” This minimizes liability under privacy and wiretap laws, especially in multistate or international operations.