A first user associated with a structure (e.g., a home, a building, etc.) may authorize a second user to access the structure when the first user is not present. The second user may request to access the structure via a text message that includes an access code that was previously provided. The second user may be verified/authenticated based on the telephone number in which the text message was received, the access code, and/or an access schedule that indicates when the second user is authorized to access the structure. The second user may send a second text message indicating a desire to lock/unlock a structure entrance (e.g., a door) to the structure that contains a smart lock. Upon receiving the second text message, a service provider sends an instruction to the smart lock, causing the structure entrance to become locked/unlocked, and allowing the second user to access or secure the structure.