Top-right indexing radical 戈 (halberd) — provides the weapon being held in vigilance. Same weapon family as 战 (war), 戎 (army), 戍 (garrison). The halberd makes 戒 fundamentally a martial-vigilance character before its abstract senses.
Bottom 廾 — two hands clasped, gripping the halberd above. The whole oracle-bone scene shows a sentry on alert, weapon raised, both hands ready. From standing guard came guard against, abstain from, warn — and the finger ring as a wearable reminder.
