The lower rating is due to the company's impending sale to private equity firm Apollo Global Management (APO).
The 40-day "Go Shop" period for the merger agreement ended on March 28.
The acquisition is expected to be completed as intended and close sometime in June, Credit Suisse noted.
Additionally, ADT had disappointing gross add results in the first quarter, declining by 1%, due to its new customer acquisition strategy to enhance the quality of its customer base, the firm said.
"Management was confident their guidance of positive net adds for the year was still possible despite the shortfall to the start of the year," Credit Suisse wrote in a note.
Boca Raton, FL-based ADT is a provider of monitored security and interactive home and business automation.
Shares of ADT are lower by 0.15% to $41.23 on Tuesday morning.
Separately, TheStreet Ratings Team has a "Hold" rating with a score of C+ on ADT stock.
The primary factors that have impacted our rating are mixed.
The company's strengths can be seen in multiple areas, such as its revenue growth, reasonable valuation levels and good cash flow from operations.
However, the team also finds that the company has favored debt over equity in the management of its balance sheet.
Recently, TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this articles's author.