diff --git a/crates/engine/src/ext.rs b/crates/engine/src/ext.rs
index ecfcc59be73..d784d12094b 100644
--- a/crates/engine/src/ext.rs
+++ b/crates/engine/src/ext.rs
@@ -257,6 +257,17 @@ impl Engine {
         }
     }
 
+    /// Returns the size of the value stored in the contract storage at the key if any.
+    pub fn contains_storage(&mut self, key: &[u8; 32]) -> Option<u32> {
+        let callee = self.get_callee();
+        let account_id = AccountId::from_bytes(&callee[..]);
+
+        self.debug_info.inc_reads(account_id);
+        self.database
+            .get_from_contract_storage(&callee, key)
+            .map(|val| val.len() as u32)
+    }
+
     /// Removes the storage entries at the given key.
     pub fn clear_storage(&mut self, key: &[u8; 32]) {
         let callee = self.get_callee();
diff --git a/crates/env/src/engine/off_chain/impls.rs b/crates/env/src/engine/off_chain/impls.rs
index 63e312b9f58..26e1e3b4f1a 100644
--- a/crates/env/src/engine/off_chain/impls.rs
+++ b/crates/env/src/engine/off_chain/impls.rs
@@ -206,10 +206,8 @@ impl EnvBackend for EnvInstance {
         Ok(Some(decoded))
     }
 
-    fn contract_storage_contains(&mut self, _key: &Key) -> Option<u32> {
-        unimplemented!(
-            "the off-chain env does not implement `seal_contains_storage`, yet"
-        )
+    fn contract_storage_contains(&mut self, key: &Key) -> Option<u32> {
+        self.engine.contains_storage(key.as_ref())
     }
 
     fn clear_contract_storage(&mut self, key: &Key) {
diff --git a/crates/storage/src/lazy/mapping.rs b/crates/storage/src/lazy/mapping.rs
index 0f1a80631e7..a704217f0ca 100644
--- a/crates/storage/src/lazy/mapping.rs
+++ b/crates/storage/src/lazy/mapping.rs
@@ -161,13 +161,24 @@ where
     ///
     /// Returns `None` if no `value` exists at the given `key`.
     #[inline]
-    pub fn contains<Q>(&self, key: Q) -> Option<u32>
+    pub fn size<Q>(&self, key: Q) -> Option<u32>
     where
         Q: scale::EncodeLike<K>,
     {
         ink_env::contract_storage_contains(&self.storage_key(&key))
     }
 
+    /// Checks if a value is stored at the given `key` in the contract storage.
+    ///
+    /// Returns `None` if no `value` exists at the given `key`.
+    #[inline]
+    pub fn contains<Q>(&self, key: Q) -> bool
+    where
+        Q: scale::EncodeLike<K>,
+    {
+        ink_env::contract_storage_contains(&self.storage_key(&key)).is_some()
+    }
+
     /// Clears the value at `key` from storage.
     pub fn remove<Q>(&self, key: Q)
     where
diff --git a/examples/dns/lib.rs b/examples/dns/lib.rs
index 6a54f4a2213..7a389da1c0f 100644
--- a/examples/dns/lib.rs
+++ b/examples/dns/lib.rs
@@ -96,7 +96,7 @@ mod dns {
         #[ink(message)]
         pub fn register(&mut self, name: Hash) -> Result<()> {
             let caller = self.env().caller();
-            if self.name_to_owner.get(&name).is_some() {
+            if self.name_to_owner.contains(&name) {
                 return Err(Error::NameAlreadyExists)
             }
 
diff --git a/examples/erc1155/lib.rs b/examples/erc1155/lib.rs
index 0c9a3f432a2..12d68f78d55 100644
--- a/examples/erc1155/lib.rs
+++ b/examples/erc1155/lib.rs
@@ -539,7 +539,7 @@ mod erc1155 {
 
         #[ink(message)]
         fn is_approved_for_all(&self, owner: AccountId, operator: AccountId) -> bool {
-            self.approvals.get((&owner, &operator)).is_some()
+            self.approvals.contains((&owner, &operator))
         }
     }
 
diff --git a/examples/erc721/lib.rs b/examples/erc721/lib.rs
index 4d528e73ac6..0bc88fad932 100644
--- a/examples/erc721/lib.rs
+++ b/examples/erc721/lib.rs
@@ -283,7 +283,7 @@ mod erc721 {
                 ..
             } = self;
 
-            if token_owner.get(&id).is_none() {
+            if !token_owner.contains(&id) {
                 return Err(Error::TokenNotFound)
             }
 
@@ -305,7 +305,7 @@ mod erc721 {
                 ..
             } = self;
 
-            if token_owner.get(&id).is_some() {
+            if token_owner.contains(&id) {
                 return Err(Error::TokenExists)
             }
 
@@ -360,7 +360,7 @@ mod erc721 {
                 return Err(Error::NotAllowed)
             };
 
-            if self.token_approvals.get(&id).is_some() {
+            if self.token_approvals.contains(&id) {
                 return Err(Error::CannotInsert)
             } else {
                 self.token_approvals.insert(&id, to);
@@ -387,7 +387,7 @@ mod erc721 {
 
         /// Gets an operator on other Account's behalf.
         fn approved_for_all(&self, owner: AccountId, operator: AccountId) -> bool {
-            self.operator_approvals.get((&owner, &operator)).is_some()
+            self.operator_approvals.contains((&owner, &operator))
         }
 
         /// Returns true if the `AccountId` `from` is the owner of token `id`
@@ -405,7 +405,7 @@ mod erc721 {
 
         /// Returns true if token `id` exists or false if it does not.
         fn exists(&self, id: TokenId) -> bool {
-            self.token_owner.get(&id).is_some()
+            self.token_owner.contains(&id)
         }
     }
 
diff --git a/examples/multisig/lib.rs b/examples/multisig/lib.rs
index 0e3ca6a9bce..afb8a2a3deb 100755
--- a/examples/multisig/lib.rs
+++ b/examples/multisig/lib.rs
@@ -504,7 +504,7 @@ mod multisig {
         pub fn revoke_confirmation(&mut self, trans_id: TransactionId) {
             self.ensure_caller_is_owner();
             let caller = self.env().caller();
-            if self.confirmations.get(&(trans_id, caller)).is_some() {
+            if self.confirmations.contains(&(trans_id, caller)) {
                 self.confirmations.remove(&(trans_id, caller));
                 let mut confirmation_count = self
                     .confirmation_count
@@ -601,7 +601,7 @@ mod multisig {
         ) -> ConfirmationStatus {
             let mut count = self.confirmation_count.get(&transaction).unwrap_or(0);
             let key = (transaction, confirmer);
-            let new_confirmation = self.confirmations.get(&key).is_none();
+            let new_confirmation = !self.confirmations.contains(&key);
             if new_confirmation {
                 count += 1;
                 self.confirmations.insert(&key, &());
@@ -659,7 +659,7 @@ mod multisig {
         fn clean_owner_confirmations(&mut self, owner: &AccountId) {
             for trans_id in &self.transaction_list.transactions {
                 let key = (*trans_id, *owner);
-                if self.confirmations.get(&key).is_some() {
+                if self.confirmations.contains(&key) {
                     self.confirmations.remove(&key);
                     let mut count = self.confirmation_count.get(&trans_id).unwrap_or(0);
                     count -= 1;
@@ -696,12 +696,12 @@ mod multisig {
 
         /// Panic if `owner` is not an owner,
         fn ensure_owner(&self, owner: &AccountId) {
-            assert!(self.is_owner.get(owner).is_some());
+            assert!(self.is_owner.contains(owner));
         }
 
         /// Panic if `owner` is an owner.
         fn ensure_no_owner(&self, owner: &AccountId) {
-            assert!(self.is_owner.get(owner).is_none());
+            assert!(!self.is_owner.contains(owner));
         }
     }
 
@@ -794,12 +794,12 @@ mod multisig {
             assert_eq!(contract.owners.len(), 3);
             assert_eq!(contract.requirement, 2);
             assert!(contract.owners.iter().eq(owners.iter()));
-            assert!(contract.is_owner.get(&accounts.alice).is_some());
-            assert!(contract.is_owner.get(&accounts.bob).is_some());
-            assert!(contract.is_owner.get(&accounts.eve).is_some());
-            assert!(contract.is_owner.get(&accounts.charlie).is_none());
-            assert!(contract.is_owner.get(&accounts.django).is_none());
-            assert!(contract.is_owner.get(&accounts.frank).is_none());
+            assert!(contract.is_owner.contains(&accounts.alice));
+            assert!(contract.is_owner.contains(&accounts.bob));
+            assert!(contract.is_owner.contains(&accounts.eve));
+            assert!(!contract.is_owner.contains(&accounts.charlie));
+            assert!(!contract.is_owner.contains(&accounts.django));
+            assert!(!contract.is_owner.contains(&accounts.frank));
             assert_eq!(contract.transaction_list.transactions.len(), 0);
         }
 
@@ -831,7 +831,7 @@ mod multisig {
             let owners = contract.owners.len();
             contract.add_owner(accounts.frank);
             assert_eq!(contract.owners.len(), owners + 1);
-            assert!(contract.is_owner.get(&accounts.frank).is_some());
+            assert!(contract.is_owner.contains(&accounts.frank));
             assert_eq!(test::recorded_events().count(), 1);
         }
 
@@ -861,7 +861,7 @@ mod multisig {
             let owners = contract.owners.len();
             contract.remove_owner(accounts.alice);
             assert_eq!(contract.owners.len(), owners - 1);
-            assert!(contract.is_owner.get(&accounts.alice).is_none());
+            assert!(!contract.is_owner.contains(&accounts.alice));
             assert_eq!(test::recorded_events().count(), 1);
         }
 
@@ -891,8 +891,8 @@ mod multisig {
             let owners = contract.owners.len();
             contract.replace_owner(accounts.alice, accounts.django);
             assert_eq!(contract.owners.len(), owners);
-            assert!(contract.is_owner.get(&accounts.alice).is_none());
-            assert!(contract.is_owner.get(&accounts.django).is_some());
+            assert!(!contract.is_owner.contains(&accounts.alice));
+            assert!(contract.is_owner.contains(&accounts.django));
             assert_eq!(test::recorded_events().count(), 2);
         }
 
@@ -1053,7 +1053,7 @@ mod multisig {
             set_caller(accounts.alice);
             contract.revoke_confirmation(0);
             assert_eq!(test::recorded_events().count(), 3);
-            assert!(contract.confirmations.get(&(0, accounts.alice)).is_none());
+            assert!(!contract.confirmations.contains(&(0, accounts.alice)));
             assert_eq!(contract.confirmation_count.get(&0).unwrap(), 0);
         }
 
@@ -1064,7 +1064,7 @@ mod multisig {
             set_caller(accounts.bob);
             contract.revoke_confirmation(0);
             assert_eq!(test::recorded_events().count(), 2);
-            assert!(contract.confirmations.get(&(0, accounts.alice)).is_some());
+            assert!(contract.confirmations.contains(&(0, accounts.alice)));
             assert_eq!(contract.confirmation_count.get(&0).unwrap(), 1);
         }