As a general rule, they can enter the fugitive's property, but not anyone else's.
They must be physically aware, by sight or sound, that the fugitive is within the home, and that entering the home will not endanger anyone inside.
When someone accepts bail, they essentially form a contract in which they surrender several legal rights in return for being let out. Part of this agreement allows a bounty hunter to enter your property to re-arrest you if you attempt to escape. They do not, however, have the right to enter a third party's residence without permission, even if the fugitive is inside. The third party hasn't signed any agreement with the state, so bounty hunters have no special rights when dealing with them.
It depends on the state. In Texas they cannot enter without permission.
Sec. 1702.3867. EXECUTION OF CAPIAS OR ARREST WARRANT; OFFENSE.
(a) A private investigator executing a capias or an arrest warrant on behalf of a bail bond surety may not: (1) enter a residence without the consent of the occupants; (2) execute the capias or warrant without written authorization from the surety; (3) wear, carry, or display any uniform, badge, shield, or other insignia or emblem that implies that the private investigator is an employee, officer, or agent of the federal government, the state, or a political subdivision of the state;
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