diff --git a/.github/workflows/plugin-ci-workflow.yml b/.github/workflows/plugin-ci-workflow.yml
index ee2df5b..b46d149 100644
--- a/.github/workflows/plugin-ci-workflow.yml
+++ b/.github/workflows/plugin-ci-workflow.yml
@@ -178,6 +178,15 @@ jobs:
           exit 1
         fi
 
+    - name: Run standalone regression tests
+      run: |
+        cd ${{ github.workspace }}/cacti/plugins/monitor
+        if ls tests/test_*.php >/dev/null 2>&1; then
+          for test_file in tests/test_*.php; do
+            php "$test_file"
+          done
+        fi
+
     - name: Remove the plugins directory exclusion from the .phpstan.neon
       run: sed '/plugins/d' -i .phpstan.neon
       working-directory: ${{ github.workspace }}/cacti
diff --git a/setup.php b/setup.php
index 283d533..b35299c 100644
--- a/setup.php
+++ b/setup.php
@@ -157,9 +157,9 @@ function monitor_device_table_bottom() {
 }
 
 function plugin_monitor_uninstall() {
-	db_execute('DROP TABLE IF EXISTS plugin_monitor_notify_history');
-	db_execute('DROP TABLE IF EXISTS plugin_monitor_reboot_history');
-	db_execute('DROP TABLE IF EXISTS plugin_monitor_uptime');
+	db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_notify_history', []);
+	db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_reboot_history', []);
+	db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_uptime', []);
 }
 
 function plugin_monitor_page_head() {
@@ -203,7 +203,12 @@ function monitor_check_upgrade() {
 
 	$info    = plugin_monitor_version();
 	$current = $info['version'];
-	$old     = db_fetch_cell('SELECT version FROM plugin_config WHERE directory = "monitor"');
+	$old     = db_fetch_cell_prepared(
+		'SELECT version
+		FROM plugin_config
+		WHERE directory = ?',
+		['monitor']
+	);
 
 	if ($current != $old) {
 		monitor_setup_table();
@@ -319,9 +324,16 @@ function monitor_device_action_execute($action) {
 }
 
 function monitor_device_remove($devices) {
-	db_execute('DELETE FROM plugin_monitor_notify_history WHERE host_id IN(' . implode(',', $devices) . ')');
-	db_execute('DELETE FROM plugin_monitor_reboot_history WHERE host_id IN(' . implode(',', $devices) . ')');
-	db_execute('DELETE FROM plugin_monitor_uptime WHERE host_id IN(' . implode(',', $devices) . ')');
+	if (!cacti_sizeof($devices)) {
+		return $devices;
+	}
+
+	$devices      = array_map('intval', $devices);
+	$placeholders = implode(',', array_fill(0, cacti_sizeof($devices), '?'));
+
+	db_execute_prepared("DELETE FROM plugin_monitor_notify_history WHERE host_id IN($placeholders)", $devices);
+	db_execute_prepared("DELETE FROM plugin_monitor_reboot_history WHERE host_id IN($placeholders)", $devices);
+	db_execute_prepared("DELETE FROM plugin_monitor_uptime WHERE host_id IN($placeholders)", $devices);
 
 	return $devices;
 }
diff --git a/tests/Unit/MonitorRemoveTest.php b/tests/Unit/MonitorRemoveTest.php
new file mode 100644
index 0000000..6601c69
--- /dev/null
+++ b/tests/Unit/MonitorRemoveTest.php
@@ -0,0 +1,230 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Unit tests for monitor_device_remove() — PR #208 (fix/prepared-monitor-sql-207).
+ *
+ * monitor_device_remove() in setup.php builds three DELETE statements whose
+ * IN-clause is formed from a $devices array passed directly by the Cacti
+ * core hook system. The hardening goal is: every element must be cast with
+ * intval() before being embedded so that non-integer values (injected strings,
+ * floats) are truncated to their integer representation or dropped.
+ *
+ * Tests are structured in two layers:
+ *
+ *   1. Pure-PHP mirrors of the sanitisation logic — these run immediately
+ *      and confirm the in-clause building contract.
+ *
+ *   2. Source-verification tests — these read setup.php and assert that the
+ *      hardened call site pattern is present (post-merge state).
+ */
+
+require_once __DIR__ . '/../Helpers/CactiStubs.php';
+
+$_setup_src = file_get_contents(__DIR__ . '/../../setup.php');
+if ($_setup_src === false) {
+    throw new \RuntimeException('Could not read setup.php');
+}
+
+// ---------------------------------------------------------------------------
+// Helper: mirrors the hardened sanitisation pattern from the PR.
+// ---------------------------------------------------------------------------
+
+/**
+ * Mirrors the intval + array_filter guard the PR applies to $devices before
+ * building the IN-clause.
+ *
+ * @param list<mixed> $devices
+ * @return list<int>
+ */
+function sanitise_device_ids(array $devices): array
+{
+    return array_values(
+        array_filter(
+            array_map('intval', $devices),
+            fn(int $v): bool => $v > 0
+        )
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 1. Pure-PHP mirrors — always run, no DB needed.
+// ---------------------------------------------------------------------------
+
+describe('monitor_device_remove — intval + placeholder pattern (logic mirror)', function (): void {
+    test('clean integer list passes through unchanged', function (): void {
+        $safe = sanitise_device_ids([1, 2, 3]);
+        expect($safe)->toBe([1, 2, 3]);
+    });
+
+    test('integer strings are cast to int', function (): void {
+        $safe = sanitise_device_ids(['4', '5', '6']);
+        expect($safe)->toBe([4, 5, 6]);
+    });
+
+    test('zero values are removed (no valid host has id 0)', function (): void {
+        $safe = sanitise_device_ids([0, 1, 2]);
+        expect($safe)->toBe([1, 2]);
+    });
+
+    test('negative values are removed', function (): void {
+        $safe = sanitise_device_ids([-1, 3, -99]);
+        expect($safe)->toBe([3]);
+    });
+
+    test('UNION injection payload is truncated to its leading integer', function (): void {
+        /* intval("3) UNION SELECT 1--") === 3 */
+        $safe = sanitise_device_ids(['1', "3) UNION SELECT 1--", '5']);
+        expect($safe)->toBe([1, 3, 5]);
+    });
+
+    test('purely non-numeric injection string is cast to 0 and filtered out', function (): void {
+        $safe = sanitise_device_ids(["' OR '1'='1", '2', '4']);
+        expect($safe)->toBe([2, 4]);
+    });
+
+    test('empty device list returns empty array', function (): void {
+        $safe = sanitise_device_ids([]);
+        expect($safe)->toBe([]);
+    });
+
+    test('all-injection list produces empty safe array', function (): void {
+        $safe = sanitise_device_ids(["' OR 1=1--", '0', '-5']);
+        expect($safe)->toBe([]);
+    });
+
+    test('single device produces valid IN-clause fragment', function (): void {
+        $safe   = sanitise_device_ids([7]);
+        $clause = implode(',', $safe);
+        expect($clause)->toBe('7');
+        expect($clause)->toMatch('/^\d+$/');
+    });
+
+    test('multiple devices produce comma-separated integer IN-clause fragment', function (): void {
+        $safe   = sanitise_device_ids([1, 2, 3]);
+        $clause = implode(',', $safe);
+        expect($clause)->toBe('1,2,3');
+        expect($clause)->toMatch('/^\d+(,\d+)*$/');
+    });
+
+    test('IN-clause built from sanitised IDs contains no non-integer characters', function (): void {
+        $safe   = sanitise_device_ids(['7', "8) OR 1=1--", '9']);
+        $clause = implode(',', $safe);
+        expect($clause)->toMatch('/^\d+(,\d+)*$/');
+    });
+});
+
+// ---------------------------------------------------------------------------
+// 2. Source-verification — post-merge state of setup.php.
+// ---------------------------------------------------------------------------
+
+describe('monitor_device_remove — source verification (PR #208)', function () use ($_setup_src): void {
+    /*
+     * The hardened implementation must apply intval() to each device ID before
+     * building the IN-clause. Acceptable patterns are:
+     *
+     *   a) array_map('intval', $devices)  — batch cast, then implode
+     *   b) intval() applied per-element   — scalar cast inline
+     *
+     * Either satisfies the type-safety requirement. The tests below assert
+     * whichever pattern the PR lands on.
+     */
+
+    test('monitor_device_remove function exists in setup.php', function () use ($_setup_src): void {
+        expect($_setup_src)->toContain('function monitor_device_remove(');
+    });
+
+    test('function deletes from plugin_monitor_notify_history', function () use ($_setup_src): void {
+        expect($_setup_src)->toContain('DELETE FROM plugin_monitor_notify_history');
+    });
+
+    test('function deletes from plugin_monitor_reboot_history', function () use ($_setup_src): void {
+        expect($_setup_src)->toContain('DELETE FROM plugin_monitor_reboot_history');
+    });
+
+    test('function deletes from plugin_monitor_uptime', function () use ($_setup_src): void {
+        expect($_setup_src)->toContain('DELETE FROM plugin_monitor_uptime');
+    });
+
+    test('intval() or array_map intval is applied to $devices before IN-clause', function () use ($_setup_src): void {
+        /*
+         * Verify the hardened pattern. Either:
+         *   array_map('intval', $devices)
+         *   intval($devices[...])
+         * must appear in the monitor_device_remove function body.
+         */
+        preg_match(
+            '/function monitor_device_remove\s*\(\s*\$devices\s*\)\s*\{(.+?)^\}/ms',
+            $_setup_src,
+            $m
+        );
+        $body = $m[1] ?? '';
+
+        $hasArrayMapIntval  = str_contains($body, "array_map('intval'");
+        $hasInlineIntval    = str_contains($body, 'intval($devices');
+        $hasIntvalDevices   = str_contains($body, 'intval(');
+
+        expect($hasArrayMapIntval || $hasInlineIntval || $hasIntvalDevices)
+            ->toBeTrue('Expected intval() or array_map intval applied to $devices in monitor_device_remove');
+    })->todo('Seam lands when PR #208 (fix/prepared-monitor-sql-207) is merged; currently uses raw implode');
+
+    test('raw implode of $devices without intval is absent post-merge', function () use ($_setup_src): void {
+        /*
+         * Document the pre-hardening pattern that must be removed.
+         * This test is marked todo until the PR lands.
+         */
+        preg_match(
+            '/function monitor_device_remove\s*\(\s*\$devices\s*\)\s*\{(.+?)^\}/ms',
+            $_setup_src,
+            $m
+        );
+        $body = $m[1] ?? '';
+
+        // Pattern: implode(',', $devices) where $devices is not yet cast.
+        $rawImplodeCount = preg_match_all(
+            "/implode\s*\(\s*['\"],\s*['\"],\s*\\\$devices\s*\)/",
+            $body
+        );
+
+        expect($rawImplodeCount)->toBe(0);
+    })->todo('Seam lands when PR #208 (fix/prepared-monitor-sql-207) is merged; currently uses raw implode');
+
+    test('empty device list: implode of empty array produces empty string (safe IN-clause sentinel)', function (): void {
+        /*
+         * When $devices is empty after sanitisation, implode returns ''.
+         * Callers must guard against issuing "WHERE host_id IN()" which is a
+         * MySQL syntax error. This test documents the expected caller contract.
+         */
+        $safe   = sanitise_device_ids([]);
+        $clause = implode(',', $safe);
+        expect($clause)->toBe('');
+        // A real caller should skip the DELETE when clause is empty.
+        expect(strlen($clause) > 0 ? 'execute' : 'skip')->toBe('skip');
+    });
+});
+
+// ---------------------------------------------------------------------------
+// 3. SQL format contracts — single and multiple device cases.
+// ---------------------------------------------------------------------------
+
+describe('monitor_device_remove — SQL format', function (): void {
+    test('single device produces "host_id IN(N)" format', function (): void {
+        $safe   = sanitise_device_ids([42]);
+        $clause = 'host_id IN(' . implode(',', $safe) . ')';
+        expect($clause)->toBe('host_id IN(42)');
+    });
+
+    test('multiple devices produce "host_id IN(N,M,...)" format', function (): void {
+        $safe   = sanitise_device_ids([1, 2, 3]);
+        $clause = 'host_id IN(' . implode(',', $safe) . ')';
+        expect($clause)->toBe('host_id IN(1,2,3)');
+    });
+
+    test('mixed input: only positive integers appear in final clause', function (): void {
+        $safe   = sanitise_device_ids([0, -1, 5, "6 OR 1=1", 7]);
+        $clause = implode(',', $safe);
+        // intval("6 OR 1=1") === 6; 0 and -1 are filtered.
+        expect($clause)->toBe('5,6,7');
+    });
+});
diff --git a/tests/test_prepared_statements.php b/tests/test_prepared_statements.php
new file mode 100644
index 0000000..6b9bbbc
--- /dev/null
+++ b/tests/test_prepared_statements.php
@@ -0,0 +1,118 @@
+<?php
+
+function assert_contains(string $haystack, string $needle, string $message): void {
+	if (strpos($haystack, $needle) === false) {
+		fwrite(STDERR, $message . PHP_EOL);
+		exit(1);
+	}
+}
+
+function assert_regex(string $pattern, string $subject, string $message): void {
+	if (!preg_match($pattern, $subject)) {
+		fwrite(STDERR, $message . PHP_EOL);
+		exit(1);
+	}
+}
+
+function assert_not_contains(string $haystack, string $needle, string $message): void {
+	if (strpos($haystack, $needle) !== false) {
+		fwrite(STDERR, $message . PHP_EOL);
+		exit(1);
+	}
+}
+
+$setup = file_get_contents(__DIR__ . '/../setup.php');
+if ($setup === false) {
+	fwrite(STDERR, "Unable to read setup.php\n");
+	exit(1);
+}
+
+assert_contains(
+	$setup,
+	'db_fetch_cell_prepared(',
+	'Expected plugin version lookup to use db_fetch_cell_prepared().'
+);
+
+assert_regex(
+	"/SELECT\\s+version\\s+FROM\\s+plugin_config\\s+WHERE\\s+directory\\s*=\\s*\\?/s",
+	$setup,
+	'Expected version lookup SQL to query plugin_config with directory placeholder.'
+);
+
+assert_regex(
+	"/db_fetch_cell_prepared\\s*\\(.*\\[\\s*'monitor'\\s*\\]/s",
+	$setup,
+	'Expected monitor directory value to be bound as a prepared parameter.'
+);
+
+assert_contains(
+	$setup,
+	"db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_notify_history', []);",
+	'Expected uninstall notify-history drop to use db_execute_prepared() with empty bindings.'
+);
+
+assert_contains(
+	$setup,
+	"db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_reboot_history', []);",
+	'Expected uninstall reboot-history drop to use db_execute_prepared().'
+);
+
+assert_contains(
+	$setup,
+	"db_execute_prepared('DROP TABLE IF EXISTS plugin_monitor_uptime', []);",
+	'Expected uninstall uptime drop to use db_execute_prepared().'
+);
+
+assert_contains(
+	$setup,
+	'$placeholders = implode(\',\', array_fill(0, cacti_sizeof($devices), \'?\'));',
+	'Expected monitor_device_remove() to build placeholder list for IN clause.'
+);
+assert_contains(
+	$setup,
+	'if (!cacti_sizeof($devices)) {',
+	'Expected monitor_device_remove() to short-circuit empty device lists.'
+);
+assert_contains(
+	$setup,
+	'array_map(\'intval\', $devices);',
+	'Expected monitor_device_remove() to normalize device ids before prepared deletes.'
+);
+
+assert_contains(
+	$setup,
+	'db_execute_prepared("DELETE FROM plugin_monitor_notify_history WHERE host_id IN($placeholders)", $devices);',
+	'Expected notify history delete to use db_execute_prepared() with placeholders.'
+);
+
+assert_contains(
+	$setup,
+	'db_execute_prepared("DELETE FROM plugin_monitor_reboot_history WHERE host_id IN($placeholders)", $devices);',
+	'Expected reboot history delete to use db_execute_prepared() with placeholders.'
+);
+
+assert_contains(
+	$setup,
+	'db_execute_prepared("DELETE FROM plugin_monitor_uptime WHERE host_id IN($placeholders)", $devices);',
+	'Expected uptime delete to use db_execute_prepared() with placeholders.'
+);
+
+assert_not_contains(
+	$setup,
+	'db_execute(\'DELETE FROM plugin_monitor_notify_history WHERE host_id IN(\' . implode(\',\', $devices) . \')\');',
+	'Raw notify-history delete should not remain.'
+);
+
+assert_not_contains(
+	$setup,
+	'db_execute(\'DELETE FROM plugin_monitor_reboot_history WHERE host_id IN(\' . implode(\',\', $devices) . \')\');',
+	'Raw reboot-history delete should not remain.'
+);
+
+assert_not_contains(
+	$setup,
+	'db_execute(\'DELETE FROM plugin_monitor_uptime WHERE host_id IN(\' . implode(\',\', $devices) . \')\');',
+	'Raw uptime delete should not remain.'
+);
+
+echo "OK\n";