diff --git a/Cargo.lock b/Cargo.lock
index b1613420..a9aadf55 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -9483,6 +9483,7 @@ dependencies = [
  "futures-util",
  "group",
  "k256",
+ "parity-scale-codec",
  "rand_core",
  "serai-client",
  "serai-ethereum-test-primitives",
diff --git a/processor/ethereum/erc20/src/lib.rs b/processor/ethereum/erc20/src/lib.rs
index 953bab88..a3ed386c 100644
--- a/processor/ethereum/erc20/src/lib.rs
+++ b/processor/ethereum/erc20/src/lib.rs
@@ -21,6 +21,7 @@ use futures_util::stream::{StreamExt, FuturesUnordered};
 #[rustfmt::skip]
 #[expect(warnings)]
 #[expect(needless_pass_by_value)]
+#[expect(missing_docs)]
 #[expect(clippy::all)]
 #[expect(clippy::ignored_unit_patterns)]
 #[expect(clippy::redundant_closure_for_method_calls)]
@@ -28,11 +29,12 @@ mod abi {
   alloy_sol_macro::sol!("contracts/IERC20.sol");
 }
 use abi::IERC20::{IERC20Calls, transferCall, transferFromCall};
-use abi::SeraiIERC20::{
-  SeraiIERC20Calls, transferWithInInstruction01BB244A8ACall as transferWithInInstructionCall,
+use abi::SeraiIERC20::SeraiIERC20Calls;
+pub use abi::IERC20::Transfer;
+pub use abi::SeraiIERC20::{
+  transferWithInInstruction01BB244A8ACall as transferWithInInstructionCall,
   transferFromWithInInstruction00081948E0Call as transferFromWithInInstructionCall,
 };
-pub use abi::IERC20::Transfer;
 
 #[cfg(test)]
 mod tests;
@@ -156,6 +158,8 @@ impl Erc20 {
           ) => Vec::from(inInstruction),
         }
       } else {
+        // We don't error here so this transfer is propagated up the stack, even without the
+        // InInstruction. In practice, Serai should acknowledge this and return it to the sender
         vec![]
       };
 
diff --git a/processor/ethereum/router/Cargo.toml b/processor/ethereum/router/Cargo.toml
index 4078ba0e..1da4fd02 100644
--- a/processor/ethereum/router/Cargo.toml
+++ b/processor/ethereum/router/Cargo.toml
@@ -39,6 +39,7 @@ ethereum-primitives = { package = "serai-processor-ethereum-primitives", path =
 ethereum-deployer = { package = "serai-processor-ethereum-deployer", path = "../deployer", default-features = false }
 erc20 = { package = "serai-processor-ethereum-erc20", path = "../erc20", default-features = false }
 
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["std"] }
 serai-client = { path = "../../../substrate/client", default-features = false, features = ["ethereum"] }
 
 futures-util = { version = "0.3", default-features = false, features = ["std"] }
diff --git a/processor/ethereum/router/src/lib.rs b/processor/ethereum/router/src/lib.rs
index 9e15c9f9..a7e0165c 100644
--- a/processor/ethereum/router/src/lib.rs
+++ b/processor/ethereum/router/src/lib.rs
@@ -24,7 +24,10 @@ use alloy_transport::{TransportErrorKind, RpcError};
 use alloy_simple_request_transport::SimpleRequest;
 use alloy_provider::{Provider, RootProvider};
 
-use serai_client::networks::ethereum::Address as SeraiAddress;
+use scale::Encode;
+use serai_client::{
+  in_instructions::primitives::Shorthand, networks::ethereum::Address as SeraiAddress,
+};
 
 use ethereum_primitives::LogIndex;
 use ethereum_schnorr::{PublicKey, Signature};
@@ -309,6 +312,8 @@ impl Router {
   }
 
   /// Construct a transaction to confirm the next key representing Serai.
+  ///
+  /// The gas price is not set and is left to the caller.
   pub fn confirm_next_serai_key(&self, sig: &Signature) -> TxLegacy {
     TxLegacy {
       to: TxKind::Call(self.address),
@@ -328,6 +333,8 @@ impl Router {
   }
 
   /// Construct a transaction to update the key representing Serai.
+  ///
+  /// The gas price is not set and is left to the caller.
   pub fn update_serai_key(&self, public_key: &PublicKey, sig: &Signature) -> TxLegacy {
     TxLegacy {
       to: TxKind::Call(self.address),
@@ -342,6 +349,37 @@ impl Router {
     }
   }
 
+  /// Construct a transaction to send coins with an InInstruction to Serai.
+  ///
+  /// If coin is an ERC20, this will not create a transaction calling the Router but will create a
+  /// top-level transfer of the ERC20 to the Router. This avoids needing to call `approve` before
+  /// publishing the transaction calling the Router.
+  ///
+  /// The gas limit and gas price are not set and are left to the caller.
+  pub fn in_instruction(&self, coin: Coin, amount: U256, in_instruction: &Shorthand) -> TxLegacy {
+    match coin {
+      Coin::Ether => TxLegacy {
+        to: self.address.into(),
+        input: abi::inInstructionCall::new((coin.into(), amount, in_instruction.encode().into()))
+          .abi_encode()
+          .into(),
+        value: amount,
+        ..Default::default()
+      },
+      Coin::Erc20(erc20) => TxLegacy {
+        to: erc20.into(),
+        input: erc20::transferWithInInstructionCall::new((
+          self.address,
+          amount,
+          in_instruction.encode().into(),
+        ))
+        .abi_encode()
+        .into(),
+        ..Default::default()
+      },
+    }
+  }
+
   /// Get the message to be signed in order to execute a series of `OutInstruction`s.
   pub fn execute_message(
     chain_id: U256,
@@ -360,6 +398,8 @@ impl Router {
   }
 
   /// Construct a transaction to execute a batch of `OutInstruction`s.
+  ///
+  /// The gas limit and gas price are not set and are left to the caller.
   pub fn execute(&self, coin: Coin, fee: U256, outs: OutInstructions, sig: &Signature) -> TxLegacy {
     // TODO
     let gas_limit = Self::EXECUTE_BASE_GAS + outs.0.iter().map(|_| 200_000 + 10_000).sum::<u64>();
@@ -383,6 +423,8 @@ impl Router {
   }
 
   /// Construct a transaction to trigger the escape hatch.
+  ///
+  /// The gas price is not set and is left to the caller.
   pub fn escape_hatch(&self, escape_to: Address, sig: &Signature) -> TxLegacy {
     TxLegacy {
       to: TxKind::Call(self.address),
@@ -393,6 +435,8 @@ impl Router {
   }
 
   /// Construct a transaction to escape coins via the escape hatch.
+  ///
+  /// The gas limit and gas price are not set and are left to the caller.
   pub fn escape(&self, coin: Coin) -> TxLegacy {
     TxLegacy {
       to: TxKind::Call(self.address),
diff --git a/processor/ethereum/router/src/tests/mod.rs b/processor/ethereum/router/src/tests/mod.rs
index d3cb4427..6426bcaf 100644
--- a/processor/ethereum/router/src/tests/mod.rs
+++ b/processor/ethereum/router/src/tests/mod.rs
@@ -18,6 +18,14 @@ use alloy_provider::{Provider, RootProvider};
 
 use alloy_node_bindings::{Anvil, AnvilInstance};
 
+use scale::Encode;
+use serai_client::{
+  primitives::SeraiAddress,
+  in_instructions::primitives::{
+    InInstruction as SeraiInInstruction, RefundableInInstruction, Shorthand,
+  },
+};
+
 use ethereum_primitives::LogIndex;
 use ethereum_schnorr::{PublicKey, Signature};
 use ethereum_deployer::Deployer;
@@ -26,7 +34,7 @@ use crate::{
   _irouter_abi::IRouterWithoutCollisions::{
     self as IRouter, IRouterWithoutCollisionsErrors as IRouterErrors,
   },
-  Coin, OutInstructions, Router, Executed, Escape,
+  Coin, InInstruction, OutInstructions, Router, Executed, Escape,
 };
 
 mod constants;
@@ -165,6 +173,8 @@ impl Test {
     let tx = ethereum_primitives::deterministically_sign(tx);
     let receipt = ethereum_test_primitives::publish_tx(&self.provider, tx.clone()).await;
     assert!(receipt.status());
+    // Only check the gas is equal when writing to a previously unallocated storage slot, as this
+    // is the highest possible gas cost and what the constant is derived from
     if self.state.key.is_none() {
       assert_eq!(
         CalldataAgnosticGas::calculate(tx.tx(), receipt.gas_used),
@@ -231,6 +241,21 @@ impl Test {
     self.verify_state().await;
   }
 
+  fn eth_in_instruction_tx(&self) -> (Coin, U256, Shorthand, TxLegacy) {
+    let coin = Coin::Ether;
+    let amount = U256::from(1);
+    let shorthand = Shorthand::Raw(RefundableInInstruction {
+      origin: None,
+      instruction: SeraiInInstruction::Transfer(SeraiAddress([0xff; 32])),
+    });
+
+    let mut tx = self.router.in_instruction(coin, amount, &shorthand);
+    tx.gas_limit = 1_000_000;
+    tx.gas_price = 100_000_000_000;
+
+    (coin, amount, shorthand, tx)
+  }
+
   fn escape_hatch_tx(&self, escape_to: Address) -> TxLegacy {
     let msg = Router::escape_hatch_message(self.chain_id, self.state.next_nonce, escape_to);
     let sig = sign(self.state.key.unwrap(), &msg);
@@ -297,7 +322,43 @@ async fn test_update_serai_key() {
 
 #[tokio::test]
 async fn test_eth_in_instruction() {
-  todo!("TODO")
+  let mut test = Test::new().await;
+  test.confirm_next_serai_key().await;
+
+  let (coin, amount, shorthand, tx) = test.eth_in_instruction_tx();
+
+  // This should fail if the value mismatches the amount
+  {
+    let mut tx = tx.clone();
+    tx.value = U256::ZERO;
+    assert!(matches!(
+      test.call_and_decode_err(tx).await,
+      IRouterErrors::AmountMismatchesMsgValue(IRouter::AmountMismatchesMsgValue {})
+    ));
+  }
+
+  let tx = ethereum_primitives::deterministically_sign(tx);
+  let receipt = ethereum_test_primitives::publish_tx(&test.provider, tx.clone()).await;
+  assert!(receipt.status());
+
+  let block = receipt.block_number.unwrap();
+  let in_instructions =
+    test.router.in_instructions_unordered(block, block, &HashSet::new()).await.unwrap();
+  assert_eq!(in_instructions.len(), 1);
+  assert_eq!(
+    in_instructions[0],
+    InInstruction {
+      id: LogIndex {
+        block_hash: *receipt.block_hash.unwrap(),
+        index_within_block: receipt.inner.logs()[0].log_index.unwrap(),
+      },
+      transaction_hash: **tx.hash(),
+      from: tx.recover_signer().unwrap(),
+      coin,
+      amount,
+      data: shorthand.encode(),
+    }
+  );
 }
 
 #[tokio::test]
@@ -379,7 +440,10 @@ async fn test_escape_hatch() {
       test.call_and_decode_err(test.confirm_next_serai_key_tx()).await,
       IRouterErrors::EscapeHatchInvoked(IRouter::EscapeHatchInvoked {})
     ));
-    // TODO inInstruction
+    assert!(matches!(
+      test.call_and_decode_err(test.eth_in_instruction_tx().3).await,
+      IRouterErrors::EscapeHatchInvoked(IRouter::EscapeHatchInvoked {})
+    ));
     // TODO execute
     // We reject further attempts to update the escape hatch to prevent the last key from being
     // able to switch from the honest escape hatch to siphoning via a malicious escape hatch (such