Antonyms of unguarded :
invulnerable, wary, inhibited, reserved, restrained, close-mouthed, laconic, quiet, reticent, taciturn, tight-lipped, uncommunicative, ambiguous, circuitous, equivocal, evasive, diplomatic, politic, tactful, civil, considerate, courteous, polite, dissembling, uncandid, unforthcoming, defensible, covered, fortified, safe, screened, secure, sheltered, armed, armored, immune, impenetrable, impregnable, invincible, strong, unassailable, unbeatable, unconquerable, almighty, omnipotent, guarded, protected, resistant, shielded, attentive, chary, observant, vigilant, watchful, foresighted, forethoughtful, provident, calculating, scheming, shrewd, thoughtful, ultracareful, ultracautious, alert, cautious, circumspect, gingerly, heedful.
Examples of usage:
In the country districts crime is practically unknown, and it is common for houses to be left unguarded, and locked doors are rare. "Wheat Growing in Australia", Australia Department of External Affairs.
Although there was no reason to suspect that anyone would harm the plane, none of them felt comfortable about leaving it unguarded. "The Golden Skull", John Blaine.
Yet the camp is unguarded. "Dusty Star", Olaf Baker.