Your competitors more than likely have their own email lists, blogs, newsletters or other digital communications that allow users to sign up and receive information from the company. You can use this to your advantage by signing up for them and keeping up with all their blog posts and emails. Anything new that your competitor has come out with will be listed in these postings and you can keep up with it. They are most likely doing the same to your newsletters and blogs in order to ensure that you don't outdo them as well.
Google Alerts is the ultimate way to keep up with anyone that uses the internet. Any time a blog post, forum post, website article or other posting is made containing the keywords you enter, you will receive an email informing you of this. You can choose to receive the emails daily so that you get a complete list of all postings containing the keywords. In this case, the keywords can be your competitor's name or brand that you wish to keep up with. You can create multiple alerts in order to keep up with multiple keywords.
Analytics are generally meant for you to keep track of your own site's stats and traffic, but it can be used to keep track of your competitor's stats and traffic as well. This gives you clues as to where their traffic is coming from and what's bringing them there. This way, you can change your methods if necessary in order to more closely compete with your competitor.
Anyone who wants to be successful is using some form of social media- whether it's Twitter, Facebook, LinkedIn, Google+, or other social networks. The benefits and probabilities of success are far too great to ignore. If your competitor is on any of these social networks, you need to follow them or befriend them in order to keep up with their posts.