Conversation so far:
What were Alexander Graham Bell's later inventions?
Bell worked extensively in medical research and invented techniques for teaching speech to the deaf.
What ideas did he have regarding teaching speech to the deaf?
CANNOTANSWER.
Were there any other inventions?
The range of Bell's inventive genius is represented only in part by the 18 patents granted in his name alone and the 12 he shared with his collaborators.
These included.

Question: What do he hold these patents for?
Self-contained rewrite: What do Alexander Graham Bell hold 30 patents for?