be at someone’s service—
1. be ready to help or assist a person:
- I am at your service whenever you should need my advice.
2. (of things) be at smb.’s disposal or ready to be used:
- My car is at your service to take you around Rome and its surroundings.
Note: The expression is not equivalent in meaning to the phrase be of service to someone—be helpful to a person:
- On many occasions he was of service to me, always in kindly, unobtrusive ways.
be in someone’s service—be working as smb.’s domestic servant:
- Miss White has been in our service for five years.