Watch A
Seiko Prospex SPB155 (Baby Alpinist)
Round · 38mm · 46mm lug-to-lug
Optimal proportions for most wrists
Case: 38mmLug-to-lug: 46mmLug width: 20mmThickness: 12.9mm
Open this size in the full fit chart →Seiko Prospex SPB155 (Baby Alpinist) vs Seiko Prospex Speedtimer
Side-by-side comparison of specifications and features
Key Differences
Best Value
Seiko Prospex (Ref. SPB155 (Baby Alpinist))
Starting from $430
Best Water Resistance
Seiko Prospex (Ref. SPB155 (Baby Alpinist))
200m (2x more)
Slimmest
Seiko Prospex (Ref. SPB155 (Baby Alpinist))
12.9mm thick
See Both Watches on Your Wrist
Set your wrist circumference to compare relative case presence. Lug-to-lug is included when the catalog has it.
Medium (6.7″)
Balanced
Watch B
Seiko Prospex Speedtimer
Round · 39mm
Optimal proportions for most wrists
Case: 39mmLug width: 20mmThickness: 13.7mm
Open this size in the full fit chart →Proportional guide only: wrist shape, strap articulation, bezel design, and case curvature change how a watch actually wears.
Price Comparison
Seiko Prospex
MSRP
$725
New
$430
Used
$386
Seiko Prospex Speedtimer
MSRP
$725
New
$856
Used
$615
MSRP New (Amazon) Used (eBay)
Side-by-Side Specs
Start with the specifications that meaningfully differ. Expand the complete table for reference details and missing-data context.
| Specification | Seiko Prospex | Seiko Prospex Speedtimer |
|---|---|---|
| Pricing | ||
| New PriceProspex is $426.3 less based on the current snapshot | $430 | $856 |
| Used Price (Low)Prospex is $229.4 less at the low end | $386 | $615 |
| Used Price (High) | $2,426 | $1,607 |
| 30-Day Trend | ↑ +75.8% | ↑ +0.7% |
| Used Price Range | $386 - $2,426 | $615 - $1,607 |
| Identity | ||
| Style | Field, Sports, Tool | Chronograph, Sports |
| Dimensions | ||
| DiameterProspex is 1mm smaller | 38mm | 39mm |
| ThicknessProspex is 0.8mm thinner | 12.9mm | 13.7mm |
| Movement | ||
| Movement | Automatic | Solar Powered |
| Case | ||
| Water ResistanceProspex adds 100m water resistance | 200m (diving) | 100m (recreational diving) |
| Bezel | Fixed | Tachymeter |
| Dial | ||
| Dial Color | Green | White |
5 specifications both watches share
MSRP$725
Lug Width20mm
Case MaterialStainless Steel
CrystalSapphire Crystal
Luminous✓ Included
2 fields are excluded from the differences view because one watch lacks comparable data. Use “All specs” to inspect those gaps.
Which Should You Buy?
This Seiko Prospex SPB155 (Baby Alpinist) vs Seiko Prospex Speedtimer comparison is less about a universal winner and more about mechanical feel versus low-maintenance convenience, wrist presence versus easier fit, water-ready utility versus dressier everyday wear. Start with fit first — case width and lug-to-lug usually matter more than secondary features if wrist comfort is a concern.
Bottom line
Fit is a real separator here — compare case width and lug-to-lug before deciding, especially if wrist comfort matters more than headline features. Choose Seiko Prospex SPB155 (Baby Alpinist) if you prefer a mechanical watch experience and do not mind more upkeep; choose Seiko Prospex Speedtimer if you want a lower-maintenance daily watch.
Choose Seiko Prospex SPB155 (Baby Alpinist) when
Seiko Prospex SPB155 (Baby Alpinist) is a better fit for mechanical-watch enthusiasts, field styling.
Choose Seiko Prospex Speedtimer when
Seiko Prospex Speedtimer is a better fit for low-maintenance daily wear, chronograph styling.
Key Differences
Movement and upkeep
Seiko Prospex SPB155 (Baby Alpinist): automatic movement
Seiko Prospex Speedtimer: solar movement
Seiko Prospex SPB155 (Baby Alpinist) uses a automatic movement, while Seiko Prospex Speedtimer uses a solar movement — that changes day-to-day ownership, upkeep, and the overall feel on the wrist.
Size and wearability
Seiko Prospex SPB155 (Baby Alpinist): 38mm · L2L 46mm · 144g
Seiko Prospex Speedtimer: 39mm
Fit is a real separator here — compare case width and lug-to-lug before deciding, especially if wrist comfort matters more than headline features.
Water resistance
Seiko Prospex SPB155 (Baby Alpinist): 200m
Seiko Prospex Speedtimer: 100m
Water resistance is a meaningful separator here — the higher-rated option gives more flexibility for swimming or rougher daily use.
Price and value
Seiko Prospex SPB155 (Baby Alpinist): $430
Seiko Prospex Speedtimer: $725
There is a real price gap here — treat the more expensive option as an upgrade decision and confirm whether the extra spend buys something you will notice in weekly use.
Style and use case
Seiko Prospex SPB155 (Baby Alpinist): field
Seiko Prospex Speedtimer: chronograph
Seiko Prospex SPB155 (Baby Alpinist) leans more field, while Seiko Prospex Speedtimer pulls toward chronograph use case — pick the one that matches how you will actually wear it.
Crystal and materials
Seiko Prospex SPB155 (Baby Alpinist): sapphire crystal · steel
Seiko Prospex Speedtimer: sapphire crystal · steel
Materials are broadly similar, so finish, fit, and price will matter more than the materials list alone.
Choose Seiko Prospex SPB155 (Baby Alpinist) If...
- You prefer a mechanical watch experience and do not mind more upkeep.
- Swimming, beach use, or tougher daily wear is part of the plan.
- You are specifically shopping for a field style watch.
Choose Seiko Prospex Speedtimer If...
- You want a lower-maintenance daily watch.
- You are specifically shopping for a chronograph style watch.
- You are comfortable paying more for a stronger feature set.
Price and Value Notes
Seiko Prospex SPB155 (Baby Alpinist) is often the value play at current pricing, while Seiko Prospex Speedtimer makes more sense if you will use its extra features regularly.
There is a real price gap here — treat the more expensive option as an upgrade decision and confirm whether the extra spend buys something you will notice in weekly use.
Where to Check Deals
Check current deals on Amazon and eBay using the buttons below — listing prices, seller quality, and condition can change quickly.
Check current deals on Amazon and eBay
Prices change often, so compare the latest listings and condition options before you buy.
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Seiko Prospex
Check Price on AmazonOpens in new tab · Price may vary
Check Price on eBayFrom $793 · New & used listings
Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.
Seiko Prospex Speedtimer
Check Price on AmazonOpens in new tab · Price may vary
Check Price on eBayFrom $904 · New & used listings
Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.
Comparison FAQ
Which movement is easier to live with day to day?
Quartz and solar models are usually easier for grab-and-go use, while automatic and manual watches appeal more to buyers who enjoy the mechanical side of watch ownership.
Which one is better for smaller wrists?
Neither is clearly smaller: case width is 38mm vs 39mm and thickness 12.9mm vs 13.7mm. Pick on strap and looks instead — the size difference is not what will decide this for you.
Which is better for swimming or rough daily wear?
Seiko Prospex SPB155 (Baby Alpinist) — it is rated 200m versus 100m. Both are in the same broad bracket, so treat this as a tiebreaker rather than a deciding factor.
Is the more expensive one worth it?
Seiko Prospex SPB155 (Baby Alpinist) is the value pick at roughly $295 less. Pay more only if a specific difference above matters to you — otherwise the cheaper one is the smarter buy. Confirm live listings, since marketplace pricing moves.
Evidence & Method
How we compared these watches
No WatchCompared hands-on test claimed
- • Catalog specifications are normalized into the same units before differences are calculated.
- • The verdict uses only populated fields and the source-backed observations listed here.
- • Missing evidence reduces the depth of the conclusion instead of being filled with assumptions.
This page currently relies on normalized catalog fields and calculated differences. No external reviewer observation is used in its verdict.
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Seiko Prospex
Check Price on AmazonOpens in new tab · Price may vary
Check Price on eBayFrom $793 · New & used listings
Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.
Seiko Prospex Speedtimer
Check Price on AmazonOpens in new tab · Price may vary
Check Price on eBayFrom $904 · New & used listings
Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.
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