BTO Digital Lock Checklist: 4 Door Checks Before You Buy

You did not choose your BTO door, so the lock has to fit the door you were handed. Before you buy any digital lock, check four things: the door leaf thickness and material, the existing lockset and cutout, whether there is a gate and where its handle sits, and the swing direction and hinge side. Each takes a few minutes with a tape measure and your phone.

At Interlock we check the door and gate before recommending a model, because compatibility depends on more than the lock's price or features. If you would rather skip the measuring, send us photos of your door on WhatsApp and we will tell you what fits before you buy.

The 4 checks at a glance

1. Door leaf thickness and material. Is the door thick enough, and what is it made of?
2. The existing lockset and cutout. What is already in the door, and does the new lock fit that opening?
3. Gate and handle position. Is there a gate, and how close is its handle to your door?
4. Swing direction and hinge side. Which way does the door open, and which side are the hinges on?

1. How thick is your door, and what is it made of?

Door thickness decides whether a lock body can sit properly in the door. Measure across the full edge of the door at a clear section, away from the metal faceplate, and write it down in millimetres. For reference, the Interlock Mercury X6 lists 40 to 60mm as the recommended door thickness.

Material matters too, because it affects how the lock is fixed. Take a photo of the door edge and the face, and we will tell you if anything looks unusual. Our door and gate measurement guide shows exactly where to place the tape.

2. What lock is already in the door, and does the cutout fit?

Replacing a lock within your door's existing lock cutout is standard practice across HDB flats and does not involve structural changes to the door. So the question is not whether you can fit a digital lock, but which digital lock suits the opening that is already there.

Open the door and photograph the edge: you want the existing lock body, the latch and the bolts in one clear shot. The Mercury X6 is a mortise lock, so we look at the mortise body in your door before recommending it. If you are weighing lock types, see mortise lock vs rim lock vs deadbolt lock.

3. Is there a gate, and where does its handle sit?

A gate does not stop you installing a digital door lock, but the gate handle can collide with the lock handle if the gap between door and gate is too small. Close both the door and the gate, then measure the shortest distance between the parts that stick out most. For the Mercury X6, the listed minimum door-to-gate distance is above 60mm, and if there is a handlebar on the inside, the listed clearance is above 130mm.

Many BTO units are handed over without a gate, and a gate is optional. If you plan to add one later, tell us now so we can plan the door lock and gate lock as one pair. Our guide on door-to-gate distance and handle fit explains why this gap trips people up.

4. Which way does your door swing, and where are the hinges?

Swing direction and hinge side decide which side the lock body and handle sit on, and whether the handle clears the gate frame or a nearby wall when the door opens. Stand outside the door and note whether the hinges are on your left or right, and whether the door opens inward or outward.

This is where a full doorway photo helps. Stand back far enough to show the whole door, the frame and the gate if there is one. We use that photo to confirm the handle side before anything is ordered.

What to photograph, and what to measure

We keep the full list of shots in the five photos we need before recommending a digital lock. Clear phone photos are normally enough.

Door and gate together: the Mercury X6 and G3 pairing

If you want facial recognition and palm vein access on the main door and a camera-equipped lock on the gate, the Mercury X6 with the Mercury G3 gate lock is a pairing we install often. The X6 is $849 on sale (regular $899) and the G3 is $649 (regular $699) at the time of writing. Both are covered by a 1 year onsite warranty, and installation is free.

Neither lock is right for every door. The G3 needs a gate gap of 4 to 8mm, gate thickness of 25 to 40mm and at least 40mm of door-to-gate clearance. Both use 2.4GHz Wi-Fi only for remote features, and the G3 is not a replacement for a CCTV system. If your measurements do not suit the Mercury range, another brand may fit better, and we will say so. Browse digital gate locks if you want to compare options.

If we recommend a lock that cannot be properly installed on your door and no alternative works, our No-Fit, No-Fee guarantee means you are not charged.

When should you install the lock around key collection and renovation?

There is no rule that you must install on collection day. Our recommendation is to do the four checks as soon as you have your keys, because the answers shape your renovation plan, especially if you intend to add a gate. You can then fit the lock after the heavier renovation work is finished, so the lock body is not exposed to dust and knocks from contractors. Changing the door itself is a separate matter: if your renovation replaces the door and not just the lock, check with your town council first.

Not sure about your door? Send us a photo

For a wider look at digital locks on HDB doors, read our HDB digital lock guide.