A range of ebook collections permit users to create alerts for new books. Below are some selected resources. Many will require users to create an account.
Review Amazon's “Hot Releases” by category. Unfortunately though, the categories are very broad, with "Law" being one such category
Search WorldCat. Try using the keyword field if you are searching for books a particular topic.
Consult Books in Print. Publishers generally input records well before a book is published.
Read book reviews. The tab provides resources on finding book reviews. However, depending on the publication, book reviews can be published significantly after the publication of the book.
Subscribe to press catalogs offered by some publishers and publisher email lists.
Monitor blog entries in subject-area blogs. Follow a website or social media outlet that informs on new books.