The past few months have been brutal for ADT (NYSE:ADT) shareholders.

After pricing its initial public offering at $14 back in January, the home security company has seen its stock price plummet to around $8. Investors have soured on ADT's prospects -- and for good reason. In fact, here are three reasons ADT's stock price descent may not yet be over.

A man with his head down on a table in front of a plunging stock chart

2018 has been rough for ADT investors. Image source: Getty Images.

1. Intensifying competition

ADT has the most recognized brand in the home security industry, with about 95% awareness among consumers, according to some surveys. This brand recognition is perhaps ADT's biggest competitive advantage in a market where trust is paramount.

However, a new company is starting to make a name for itself: SimpliSafe. With far lower equipment costs and easy, do-it-yourself installation, SimpliSafe offers consumers an attractive value proposition. And they've been signing up in droves; more than 2 million people have already become SimpliSafe customers, making it the fastest growing home security company.

ADT is still the largest home security company in the U.S., with about 7.2 million customers. But with SimpliSafe rapidly taking share, ADT's growth -- and perhaps even its leading market position -- could come under pressure in the years ahead.

2. New entrants

ADT faces another major threat in Ring, the smart-home technology start-up (NASDAQ:AMZN) purchased earlier this year for more than $1 billion. Ring makes camera-equipped doorbells and other security video equipment, and it recently debuted a comprehensive home security system with alarm monitoring priced at only $10 per month.

Ring's equipment costs and monitoring fees drastically undercut those of ADT. In addition, Ring's home security system is expected to add full integration with Amazon's Alexa smart assistant platform. In addition, Ring's smart-home security products are likely to become a key part of Amazon's new in-home delivery service, Amazon Key. As such, ADT now needs to consider the e-commerce titan a new -- and extremely formidable -- competitor. This newfound competition with Amazon may further slow ADT's customer growth and make it much more difficult for ADT to raise prices, which could severely crimp its profit margins.

3. Debt is a burden 

ADT's nearly $10 billion in debt -- compared to only about $260 million in cash -- is another risk factor for investors. The cost to service this debt will continue to weigh on ADT's profits for the foreseeable future. And should interest rates rise -- a likely scenario based on the Federal Reserve's recent actions -- ADT's interest expense could rise along with them.

In fact, as my colleague Asit Sharma notes, one of the reasons ADT went public was because its majority owner -- private equity firm Apollo Management (NYSE:APO) -- wanted to pay down some of ADT's burdensome debt load with its IPO proceeds. But should investors buy what Apollo sold? So far, the answer has been "no," with ADT's stock price down more than 40% from its IPO price. And with competitive threats from SimpliSafe and Amazon mounting, ADT's stock price could continue to head lower in the months ahead.