diff --git a/src/screens/SentinelScreen.tsx b/src/screens/SentinelScreen.tsx
index 795d3c7..579c5b2 100644
--- a/src/screens/SentinelScreen.tsx
+++ b/src/screens/SentinelScreen.tsx
@@ -23,6 +23,7 @@ import { colors, typography, spacing, borderRadius, shadows } from '../theme/col
 import { SystemStatus, KillSwitchLog } from '../types';
 import VaultScreen from './VaultScreen';
 
+// Nautical-themed mnemonic word list (unique words only)
 const MNEMONIC_WORDS = [
   'anchor', 'harbor', 'compass', 'lighthouse', 'current', 'ocean', 'tide', 'voyage',
   'keel', 'stern', 'bow', 'mast', 'sail', 'port', 'starboard', 'reef',
@@ -30,9 +31,17 @@ const MNEMONIC_WORDS = [
   'horizon', 'sextant', 'sound', 'drift', 'wake', 'mariner', 'pilot', 'fathom',
   'buoy', 'lantern', 'harpoon', 'lagoon', 'bay', 'strait', 'riptide', 'foam',
   'coral', 'pearl', 'trident', 'ebb', 'flow', 'vault', 'cipher', 'shroud',
-  'salt', 'wave', 'grotto', 'lagoon', 'storm', 'north', 'south', 'east',
-  'west', 'ember', 'cabin', 'signal', 'ledger', 'torch', 'sanctum', 'oath',
-];
+  'salt', 'wave', 'grotto', 'storm', 'north', 'south', 'east', 'west',
+  'ember', 'cabin', 'ledger', 'torch', 'sanctum', 'oath', 'depths', 'captain',
+] as const;
+
+// Animation timing constants
+const ANIMATION_DURATION = {
+  pulse: 1200,
+  glow: 1500,
+  rotate: 30000,
+  heartbeatPress: 150,
+} as const;
 
 const generateMnemonic = (wordCount = 12) => {
   const words: string[] = [];
@@ -49,11 +58,14 @@ const splitMnemonic = (words: string[]) => [
   words.slice(8, 12),
 ];
 
+// Icon names type for type safety
+type StatusIconName = 'checkmark-circle' | 'warning' | 'alert-circle';
+
 // Status configuration with nautical theme
 const statusConfig: Record<SystemStatus, { 
   color: string; 
   label: string; 
-  icon: string;
+  icon: StatusIconName;
   description: string;
   gradientColors: [string, string];
 }> = {
@@ -123,46 +135,56 @@ export default function SentinelScreen() {
 
   useEffect(() => {
     // Pulse animation
-    Animated.loop(
+    const pulseAnimation = Animated.loop(
       Animated.sequence([
         Animated.timing(pulseAnim, {
           toValue: 1.06,
-          duration: 1200,
+          duration: ANIMATION_DURATION.pulse,
           useNativeDriver: true,
         }),
         Animated.timing(pulseAnim, {
           toValue: 1,
-          duration: 1200,
+          duration: ANIMATION_DURATION.pulse,
           useNativeDriver: true,
         }),
       ])
-    ).start();
+    );
+    pulseAnimation.start();
 
     // Glow animation
-    Animated.loop(
+    const glowAnimation = Animated.loop(
       Animated.sequence([
         Animated.timing(glowAnim, {
           toValue: 1,
-          duration: 1500,
+          duration: ANIMATION_DURATION.glow,
           useNativeDriver: true,
         }),
         Animated.timing(glowAnim, {
           toValue: 0.5,
-          duration: 1500,
+          duration: ANIMATION_DURATION.glow,
           useNativeDriver: true,
         }),
       ])
-    ).start();
+    );
+    glowAnimation.start();
 
     // Slow rotate for ship wheel
-    Animated.loop(
+    const rotateAnimation = Animated.loop(
       Animated.timing(rotateAnim, {
         toValue: 1,
-        duration: 30000,
+        duration: ANIMATION_DURATION.rotate,
         useNativeDriver: true,
       })
-    ).start();
-  }, []);
+    );
+    rotateAnimation.start();
+
+    // Cleanup animations on unmount to prevent memory leaks
+    return () => {
+      pulseAnimation.stop();
+      glowAnimation.stop();
+      rotateAnimation.stop();
+    };
+  }, [pulseAnim, glowAnim, rotateAnim]);
 
   const openVaultWithMnemonic = () => {
     const words = generateMnemonic();
@@ -230,23 +252,23 @@ export default function SentinelScreen() {
     Animated.sequence([
       Animated.timing(pulseAnim, {
         toValue: 1.15,
-        duration: 150,
+        duration: ANIMATION_DURATION.heartbeatPress,
         useNativeDriver: true,
       }),
       Animated.timing(pulseAnim, {
         toValue: 1,
-        duration: 150,
+        duration: ANIMATION_DURATION.heartbeatPress,
         useNativeDriver: true,
       }),
     ]).start();
 
-    // Add new log
+    // Add new log using functional update to avoid stale closure
     const newLog: KillSwitchLog = {
       id: Date.now().toString(),
       action: 'HEARTBEAT_CONFIRMED',
       timestamp: new Date(),
     };
-    setLogs([newLog, ...logs]);
+    setLogs((prevLogs) => [newLog, ...prevLogs]);
     
     // Reset status if warning
     if (status === 'warning') {
@@ -324,7 +346,7 @@ export default function SentinelScreen() {
                   colors={currentStatus.gradientColors}
                   style={styles.statusCircle}
                 >
-                  <Ionicons name={currentStatus.icon as any} size={56} color="#fff" />
+                  <Ionicons name={currentStatus.icon} size={56} color="#fff" />
                 </LinearGradient>
               </Animated.View>
               <Text style={[styles.statusLabel, { color: currentStatus.color }]}>
@@ -390,6 +412,8 @@ export default function SentinelScreen() {
                 style={styles.vaultAccessButton}
                 onPress={openVaultWithMnemonic}
                 activeOpacity={0.8}
+                accessibilityLabel="Open Shadow Vault"
+                accessibilityRole="button"
               >
                 <Text style={styles.vaultAccessButtonText}>Open</Text>
               </TouchableOpacity>
@@ -400,6 +424,8 @@ export default function SentinelScreen() {
               style={styles.heartbeatButton}
               onPress={handleHeartbeat}
               activeOpacity={0.9}
+              accessibilityLabel="Signal the watch - Confirm your presence"
+              accessibilityRole="button"
             >
               <LinearGradient
                 colors={[colors.nautical.teal, colors.nautical.seafoam]}
@@ -451,6 +477,8 @@ export default function SentinelScreen() {
             style={styles.vaultCloseButton}
             onPress={() => setShowVault(false)}
             activeOpacity={0.85}
+            accessibilityLabel="Close vault"
+            accessibilityRole="button"
           >
             <Ionicons name="close" size={20} color={colors.nautical.cream} />
           </TouchableOpacity>
@@ -468,15 +496,17 @@ export default function SentinelScreen() {
           style={styles.mnemonicOverlay}
           behavior={Platform.OS === 'ios' ? 'padding' : undefined}
         >
-          <LinearGradient
-            colors={[colors.sentinel.cardBackground, colors.sentinel.backgroundGradientEnd]}
-            style={styles.mnemonicCard}
-            ref={mnemonicRef}
-          >
+          <View ref={mnemonicRef} collapsable={false}>
+            <LinearGradient
+              colors={[colors.sentinel.cardBackground, colors.sentinel.backgroundGradientEnd]}
+              style={styles.mnemonicCard}
+            >
             <TouchableOpacity
               style={styles.mnemonicClose}
               onPress={() => setShowMnemonic(false)}
               activeOpacity={0.85}
+              accessibilityLabel="Close mnemonic modal"
+              accessibilityRole="button"
             >
               <Ionicons name="close" size={18} color={colors.sentinel.textSecondary} />
             </TouchableOpacity>
@@ -514,6 +544,9 @@ export default function SentinelScreen() {
               onPress={handleScreenshot}
               activeOpacity={0.85}
               disabled={isCapturing}
+              accessibilityLabel="Take screenshot backup of mnemonic"
+              accessibilityRole="button"
+              accessibilityState={{ disabled: isCapturing }}
             >
               <Text style={styles.mnemonicPrimaryText}>
                 {isCapturing ? 'CAPTURING...' : 'PHYSICAL BACKUP (SCREENSHOT)'}
@@ -523,6 +556,8 @@ export default function SentinelScreen() {
               style={styles.mnemonicSecondaryButton}
               onPress={handleEmailBackup}
               activeOpacity={0.85}
+              accessibilityLabel="Send mnemonic backup via email"
+              accessibilityRole="button"
             >
               <Text style={styles.mnemonicSecondaryText}>EMAIL BACKUP</Text>
             </TouchableOpacity>
@@ -542,12 +577,15 @@ export default function SentinelScreen() {
                   style={styles.emailSendButton}
                   onPress={handleSendEmail}
                   activeOpacity={0.85}
+                  accessibilityLabel="Send backup email"
+                  accessibilityRole="button"
                 >
                   <Text style={styles.emailSendText}>SEND EMAIL</Text>
                 </TouchableOpacity>
               </View>
             ) : null}
-          </LinearGradient>
+            </LinearGradient>
+          </View>
         </KeyboardAvoidingView>
       </Modal>
     </View>