CushonMe is a free service that automatically reviews your investments every day. The review looks at five key things:
the bad-case projected value of your investment has got substantially worse
market conditions are unusually volatile
the mix of your investment has drifted over time into a different risk / return category
We also email you a summary each month and daily results are available in the CushonMe tab when you log in to your account. The thresholds on each item are to make sure we only alert you if it's really worth it. For example, we won't bother alerting you if a new fund is launched whose charges are 0.02% lower. But if markets are becoming more volatile and there is a significant risk of loss between now and your target date, we will let you know.
Full details of the exact triggers and thresholds we use are here.